1 <!-- doc/src/sgml/plpgsql.sgml -->
4 <title><application>PL/pgSQL</application> - <acronym>SQL</acronym> Procedural Language</title>
6 <indexterm zone="plpgsql">
7 <primary>PL/pgSQL</primary>
10 <sect1 id="plpgsql-overview">
11 <title>Overview</title>
14 <application>PL/pgSQL</application> is a loadable procedural
15 language for the <productname>PostgreSQL</productname> database
16 system. The design goals of <application>PL/pgSQL</> were to create
17 a loadable procedural language that
22 can be used to create functions and trigger procedures,
27 adds control structures to the <acronym>SQL</acronym> language,
32 can perform complex computations,
37 inherits all user-defined types, functions, and operators,
42 can be defined to be trusted by the server,
54 Functions created with <application>PL/pgSQL</application> can be
55 used anywhere that built-in functions could be used.
56 For example, it is possible to
57 create complex conditional computation functions and later use
58 them to define operators or use them in index expressions.
62 In <productname>PostgreSQL</> 9.0 and later,
63 <application>PL/pgSQL</application> is installed by default.
64 However it is still a loadable module, so especially security-conscious
65 administrators could choose to remove it.
68 <sect2 id="plpgsql-advantages">
69 <title>Advantages of Using <application>PL/pgSQL</application></title>
72 <acronym>SQL</acronym> is the language <productname>PostgreSQL</>
73 and most other relational databases use as query language. It's
74 portable and easy to learn. But every <acronym>SQL</acronym>
75 statement must be executed individually by the database server.
79 That means that your client application must send each query to
80 the database server, wait for it to be processed, receive and
81 process the results, do some computation, then send further
82 queries to the server. All this incurs interprocess
83 communication and will also incur network overhead if your client
84 is on a different machine than the database server.
88 With <application>PL/pgSQL</application> you can group a block of
89 computation and a series of queries <emphasis>inside</emphasis>
90 the database server, thus having the power of a procedural
91 language and the ease of use of SQL, but with considerable
92 savings of client/server communication overhead.
96 <listitem><para> Extra round trips between
97 client and server are eliminated </para></listitem>
99 <listitem><para> Intermediate results that the client does not
100 need do not have to be marshaled or transferred between server
101 and client </para></listitem>
103 <listitem><para> Multiple rounds of query
104 parsing can be avoided </para></listitem>
107 <para> This can result in a considerable performance increase as
108 compared to an application that does not use stored functions.
112 Also, with <application>PL/pgSQL</application> you can use all
113 the data types, operators and functions of SQL.
117 <sect2 id="plpgsql-args-results">
118 <title>Supported Argument and Result Data Types</title>
121 Functions written in <application>PL/pgSQL</application> can accept
122 as arguments any scalar or array data type supported by the server,
123 and they can return a result of any of these types. They can also
124 accept or return any composite type (row type) specified by name.
125 It is also possible to declare a <application>PL/pgSQL</application>
126 function as returning <type>record</>, which means that the result
127 is a row type whose columns are determined by specification in the
128 calling query, as discussed in <xref linkend="queries-tablefunctions">.
132 <application>PL/pgSQL</> functions can be declared to accept a variable
133 number of arguments by using the <literal>VARIADIC</> marker. This
134 works exactly the same way as for SQL functions, as discussed in
135 <xref linkend="xfunc-sql-variadic-functions">.
139 <application>PL/pgSQL</> functions can also be declared to accept
140 and return the polymorphic types
141 <type>anyelement</type>, <type>anyarray</type>, <type>anynonarray</type>,
142 and <type>anyenum</>. The actual
143 data types handled by a polymorphic function can vary from call to
144 call, as discussed in <xref linkend="extend-types-polymorphic">.
145 An example is shown in <xref linkend="plpgsql-declaration-parameters">.
149 <application>PL/pgSQL</> functions can also be declared to return
150 a <quote>set</> (or table) of any data type that can be returned as
151 a single instance. Such a function generates its output by executing
152 <command>RETURN NEXT</> for each desired element of the result
153 set, or by using <command>RETURN QUERY</> to output the result of
158 Finally, a <application>PL/pgSQL</> function can be declared to return
159 <type>void</> if it has no useful return value.
163 <application>PL/pgSQL</> functions can also be declared with output
164 parameters in place of an explicit specification of the return type.
165 This does not add any fundamental capability to the language, but
166 it is often convenient, especially for returning multiple values.
167 The <literal>RETURNS TABLE</> notation can also be used in place
168 of <literal>RETURNS SETOF</>.
172 Specific examples appear in
173 <xref linkend="plpgsql-declaration-parameters"> and
174 <xref linkend="plpgsql-statements-returning">.
179 <sect1 id="plpgsql-structure">
180 <title>Structure of <application>PL/pgSQL</application></title>
183 <application>PL/pgSQL</application> is a block-structured language.
184 The complete text of a function definition must be a
185 <firstterm>block</>. A block is defined as:
188 <optional> <<<replaceable>label</replaceable>>> </optional>
190 <replaceable>declarations</replaceable> </optional>
192 <replaceable>statements</replaceable>
193 END <optional> <replaceable>label</replaceable> </optional>;
198 Each declaration and each statement within a block is terminated
199 by a semicolon. A block that appears within another block must
200 have a semicolon after <literal>END</literal>, as shown above;
201 however the final <literal>END</literal> that
202 concludes a function body does not require a semicolon.
207 A common mistake is to write a semicolon immediately after
208 <literal>BEGIN</>. This is incorrect and will result in a syntax error.
213 A <replaceable>label</replaceable> is only needed if you want to
214 identify the block for use
215 in an <literal>EXIT</> statement, or to qualify the names of the
216 variables declared in the block. If a label is given after
217 <literal>END</>, it must match the label at the block's beginning.
221 All key words are case-insensitive.
222 Identifiers are implicitly converted to lower case
223 unless double-quoted, just as they are in ordinary SQL commands.
227 Comments work the same way in <application>PL/pgSQL</> code as in
228 ordinary SQL. A double dash (<literal>--</literal>) starts a comment
229 that extends to the end of the line. A <literal>/*</literal> starts a
230 block comment that extends to the matching occurrence of
231 <literal>*/</literal>. Block comments nest.
235 Any statement in the statement section of a block
236 can be a <firstterm>subblock</>. Subblocks can be used for
237 logical grouping or to localize variables to a small group
238 of statements. Variables declared in a subblock mask any
239 similarly-named variables of outer blocks for the duration
240 of the subblock; but you can access the outer variables anyway
241 if you qualify their names with their block's label. For example:
243 CREATE FUNCTION somefunc() RETURNS integer AS $$
244 << outerblock >>
246 quantity integer := 30;
248 RAISE NOTICE 'Quantity here is %', quantity; -- Prints 30
254 quantity integer := 80;
256 RAISE NOTICE 'Quantity here is %', quantity; -- Prints 80
257 RAISE NOTICE 'Outer quantity here is %', outerblock.quantity; -- Prints 50
260 RAISE NOTICE 'Quantity here is %', quantity; -- Prints 50
270 There is actually a hidden <quote>outer block</> surrounding the body
271 of any <application>PL/pgSQL</> function. This block provides the
272 declarations of the function's parameters (if any), as well as some
273 special variables such as <literal>FOUND</literal> (see
274 <xref linkend="plpgsql-statements-diagnostics">). The outer block is
275 labeled with the function's name, meaning that parameters and special
276 variables can be qualified with the function's name.
281 It is important not to confuse the use of
282 <command>BEGIN</>/<command>END</> for grouping statements in
283 <application>PL/pgSQL</> with the similarly-named SQL commands
285 control. <application>PL/pgSQL</>'s <command>BEGIN</>/<command>END</>
286 are only for grouping; they do not start or end a transaction.
287 Functions and trigger procedures are always executed within a transaction
288 established by an outer query — they cannot start or commit that
289 transaction, since there would be no context for them to execute in.
290 However, a block containing an <literal>EXCEPTION</> clause effectively
291 forms a subtransaction that can be rolled back without affecting the
292 outer transaction. For more about that see <xref
293 linkend="plpgsql-error-trapping">.
297 <sect1 id="plpgsql-declarations">
298 <title>Declarations</title>
301 All variables used in a block must be declared in the
302 declarations section of the block.
303 (The only exceptions are that the loop variable of a <literal>FOR</> loop
304 iterating over a range of integer values is automatically declared as an
305 integer variable, and likewise the loop variable of a <literal>FOR</> loop
306 iterating over a cursor's result is automatically declared as a
311 <application>PL/pgSQL</> variables can have any SQL data type, such as
312 <type>integer</type>, <type>varchar</type>, and
317 Here are some examples of variable declarations:
322 myrow tablename%ROWTYPE;
323 myfield tablename.columnname%TYPE;
329 The general syntax of a variable declaration is:
331 <replaceable>name</replaceable> <optional> CONSTANT </optional> <replaceable>type</replaceable> <optional> NOT NULL </optional> <optional> { DEFAULT | := } <replaceable>expression</replaceable> </optional>;
333 The <literal>DEFAULT</> clause, if given, specifies the initial value assigned
334 to the variable when the block is entered. If the <literal>DEFAULT</> clause
335 is not given then the variable is initialized to the
336 <acronym>SQL</acronym> null value.
337 The <literal>CONSTANT</> option prevents the variable from being
338 assigned to, so that its value will remain constant for the duration of
340 If <literal>NOT NULL</>
341 is specified, an assignment of a null value results in a run-time
342 error. All variables declared as <literal>NOT NULL</>
343 must have a nonnull default value specified.
347 A variable's default value is evaluated and assigned to the variable
348 each time the block is entered (not just once per function call).
349 So, for example, assigning <literal>now()</literal> to a variable of type
350 <type>timestamp</type> causes the variable to have the
351 time of the current function call, not the time when the function was
358 quantity integer DEFAULT 32;
359 url varchar := 'http://mysite.com';
360 user_id CONSTANT integer := 10;
364 <sect2 id="plpgsql-declaration-parameters">
365 <title>Declaring Function Parameters</title>
368 Parameters passed to functions are named with the identifiers
369 <literal>$1</literal>, <literal>$2</literal>,
370 etc. Optionally, aliases can be declared for
371 <literal>$<replaceable>n</replaceable></literal>
372 parameter names for increased readability. Either the alias or the
373 numeric identifier can then be used to refer to the parameter value.
377 There are two ways to create an alias. The preferred way is to give a
378 name to the parameter in the <command>CREATE FUNCTION</command> command,
381 CREATE FUNCTION sales_tax(subtotal real) RETURNS real AS $$
383 RETURN subtotal * 0.06;
387 The other way, which was the only way available before
388 <productname>PostgreSQL</productname> 8.0, is to explicitly
389 declare an alias, using the declaration syntax
392 <replaceable>name</replaceable> ALIAS FOR $<replaceable>n</replaceable>;
395 The same example in this style looks like:
397 CREATE FUNCTION sales_tax(real) RETURNS real AS $$
399 subtotal ALIAS FOR $1;
401 RETURN subtotal * 0.06;
409 These two examples are not perfectly equivalent. In the first case,
410 <literal>subtotal</> could be referenced as
411 <literal>sales_tax.subtotal</>, but in the second case it could not.
412 (Had we attached a label to the inner block, <literal>subtotal</> could
413 be qualified with that label, instead.)
420 CREATE FUNCTION instr(varchar, integer) RETURNS integer AS $$
422 v_string ALIAS FOR $1;
425 -- some computations using v_string and index here
430 CREATE FUNCTION concat_selected_fields(in_t sometablename) RETURNS text AS $$
432 RETURN in_t.f1 || in_t.f3 || in_t.f5 || in_t.f7;
439 When a <application>PL/pgSQL</application> function is declared
440 with output parameters, the output parameters are given
441 <literal>$<replaceable>n</replaceable></literal> names and optional
442 aliases in just the same way as the normal input parameters. An
443 output parameter is effectively a variable that starts out NULL;
444 it should be assigned to during the execution of the function.
445 The final value of the parameter is what is returned. For instance,
446 the sales-tax example could also be done this way:
449 CREATE FUNCTION sales_tax(subtotal real, OUT tax real) AS $$
451 tax := subtotal * 0.06;
456 Notice that we omitted <literal>RETURNS real</> — we could have
457 included it, but it would be redundant.
461 Output parameters are most useful when returning multiple values.
462 A trivial example is:
465 CREATE FUNCTION sum_n_product(x int, y int, OUT sum int, OUT prod int) AS $$
473 As discussed in <xref linkend="xfunc-output-parameters">, this
474 effectively creates an anonymous record type for the function's
475 results. If a <literal>RETURNS</> clause is given, it must say
476 <literal>RETURNS record</>.
480 Another way to declare a <application>PL/pgSQL</application> function
481 is with <literal>RETURNS TABLE</>, for example:
484 CREATE FUNCTION extended_sales(p_itemno int)
485 RETURNS TABLE(quantity int, total numeric) AS $$
487 RETURN QUERY SELECT quantity, quantity * price FROM sales
488 WHERE itemno = p_itemno;
493 This is exactly equivalent to declaring one or more <literal>OUT</>
494 parameters and specifying <literal>RETURNS SETOF
495 <replaceable>sometype</></literal>.
499 When the return type of a <application>PL/pgSQL</application>
500 function is declared as a polymorphic type (<type>anyelement</type>,
501 <type>anyarray</type>, <type>anynonarray</type>, or <type>anyenum</>),
502 a special parameter <literal>$0</literal>
503 is created. Its data type is the actual return type of the function,
504 as deduced from the actual input types (see <xref
505 linkend="extend-types-polymorphic">).
506 This allows the function to access its actual return type
507 as shown in <xref linkend="plpgsql-declaration-type">.
508 <literal>$0</literal> is initialized to null and can be modified by
509 the function, so it can be used to hold the return value if desired,
510 though that is not required. <literal>$0</literal> can also be
511 given an alias. For example, this function works on any data type
512 that has a <literal>+</> operator:
515 CREATE FUNCTION add_three_values(v1 anyelement, v2 anyelement, v3 anyelement)
516 RETURNS anyelement AS $$
520 result := v1 + v2 + v3;
528 The same effect can be had by declaring one or more output parameters as
529 polymorphic types. In this case the
530 special <literal>$0</literal> parameter is not used; the output
531 parameters themselves serve the same purpose. For example:
534 CREATE FUNCTION add_three_values(v1 anyelement, v2 anyelement, v3 anyelement,
545 <sect2 id="plpgsql-declaration-alias">
546 <title><literal>ALIAS</></title>
549 <replaceable>newname</> ALIAS FOR <replaceable>oldname</>;
553 The <literal>ALIAS</> syntax is more general than is suggested in the
554 previous section: you can declare an alias for any variable, not just
555 function parameters. The main practical use for this is to assign
556 a different name for variables with predetermined names, such as
557 <varname>NEW</varname> or <varname>OLD</varname> within
566 updated ALIAS FOR new;
571 Since <literal>ALIAS</> creates two different ways to name the same
572 object, unrestricted use can be confusing. It's best to use it only
573 for the purpose of overriding predetermined names.
577 <sect2 id="plpgsql-declaration-type">
578 <title>Copying Types</title>
581 <replaceable>variable</replaceable>%TYPE
585 <literal>%TYPE</literal> provides the data type of a variable or
586 table column. You can use this to declare variables that will hold
587 database values. For example, let's say you have a column named
588 <literal>user_id</literal> in your <literal>users</literal>
589 table. To declare a variable with the same data type as
590 <literal>users.user_id</> you write:
592 user_id users.user_id%TYPE;
597 By using <literal>%TYPE</literal> you don't need to know the data
598 type of the structure you are referencing, and most importantly,
599 if the data type of the referenced item changes in the future (for
600 instance: you change the type of <literal>user_id</>
601 from <type>integer</type> to <type>real</type>), you might not need
602 to change your function definition.
606 <literal>%TYPE</literal> is particularly valuable in polymorphic
607 functions, since the data types needed for internal variables can
608 change from one call to the next. Appropriate variables can be
609 created by applying <literal>%TYPE</literal> to the function's
610 arguments or result placeholders.
615 <sect2 id="plpgsql-declaration-rowtypes">
616 <title>Row Types</title>
619 <replaceable>name</replaceable> <replaceable>table_name</replaceable><literal>%ROWTYPE</literal>;
620 <replaceable>name</replaceable> <replaceable>composite_type_name</replaceable>;
624 A variable of a composite type is called a <firstterm>row</>
625 variable (or <firstterm>row-type</> variable). Such a variable
626 can hold a whole row of a <command>SELECT</> or <command>FOR</>
627 query result, so long as that query's column set matches the
628 declared type of the variable.
629 The individual fields of the row value
630 are accessed using the usual dot notation, for example
631 <literal>rowvar.field</literal>.
635 A row variable can be declared to have the same type as the rows of
636 an existing table or view, by using the
637 <replaceable>table_name</replaceable><literal>%ROWTYPE</literal>
638 notation; or it can be declared by giving a composite type's name.
639 (Since every table has an associated composite type of the same name,
640 it actually does not matter in <productname>PostgreSQL</> whether you
641 write <literal>%ROWTYPE</literal> or not. But the form with
642 <literal>%ROWTYPE</literal> is more portable.)
646 Parameters to a function can be
647 composite types (complete table rows). In that case, the
648 corresponding identifier <literal>$<replaceable>n</replaceable></> will be a row variable, and fields can
649 be selected from it, for example <literal>$1.user_id</literal>.
653 Only the user-defined columns of a table row are accessible in a
654 row-type variable, not the OID or other system columns (because the
655 row could be from a view). The fields of the row type inherit the
656 table's field size or precision for data types such as
657 <type>char(<replaceable>n</>)</type>.
661 Here is an example of using composite types. <structname>table1</>
662 and <structname>table2</> are existing tables having at least the
666 CREATE FUNCTION merge_fields(t_row table1) RETURNS text AS $$
668 t2_row table2%ROWTYPE;
670 SELECT * INTO t2_row FROM table2 WHERE ... ;
671 RETURN t_row.f1 || t2_row.f3 || t_row.f5 || t2_row.f7;
675 SELECT merge_fields(t.*) FROM table1 t WHERE ... ;
680 <sect2 id="plpgsql-declaration-records">
681 <title>Record Types</title>
684 <replaceable>name</replaceable> RECORD;
688 Record variables are similar to row-type variables, but they have no
689 predefined structure. They take on the actual row structure of the
690 row they are assigned during a <command>SELECT</> or <command>FOR</> command. The substructure
691 of a record variable can change each time it is assigned to.
692 A consequence of this is that until a record variable is first assigned
693 to, it has no substructure, and any attempt to access a
694 field in it will draw a run-time error.
698 Note that <literal>RECORD</> is not a true data type, only a placeholder.
699 One should also realize that when a <application>PL/pgSQL</application>
700 function is declared to return type <type>record</>, this is not quite the
701 same concept as a record variable, even though such a function might
702 use a record variable to hold its result. In both cases the actual row
703 structure is unknown when the function is written, but for a function
704 returning <type>record</> the actual structure is determined when the
705 calling query is parsed, whereas a record variable can change its row
706 structure on-the-fly.
711 <sect1 id="plpgsql-expressions">
712 <title>Expressions</title>
715 All expressions used in <application>PL/pgSQL</application>
716 statements are processed using the server's main
717 <acronym>SQL</acronym> executor. For example, when you write
718 a <application>PL/pgSQL</application> statement like
720 IF <replaceable>expression</replaceable> THEN ...
722 <application>PL/pgSQL</application> will evaluate the expression by
725 SELECT <replaceable>expression</replaceable>
727 to the main SQL engine. While forming the <command>SELECT</> command,
728 any occurrences of <application>PL/pgSQL</application> variable names
729 are replaced by parameters, as discussed in detail in
730 <xref linkend="plpgsql-var-subst">.
731 This allows the query plan for the <command>SELECT</command> to
732 be prepared just once and then reused for subsequent
733 evaluations with different values of the variables. Thus, what
734 really happens on first use of an expression is essentially a
735 <command>PREPARE</> command. For example, if we have declared
736 two integer variables <literal>x</> and <literal>y</>, and we write
740 what happens behind the scenes is equivalent to
742 PREPARE <replaceable>statement_name</>(integer, integer) AS SELECT $1 < $2;
744 and then this prepared statement is <command>EXECUTE</>d for each
745 execution of the <command>IF</> statement, with the current values
746 of the <application>PL/pgSQL</application> variables supplied as
748 The query plan prepared in this way is saved for the life of the database
749 connection, as described in
750 <xref linkend="plpgsql-plan-caching">. Normally these details are
751 not important to a <application>PL/pgSQL</application> user, but
752 they are useful to know when trying to diagnose a problem.
756 <sect1 id="plpgsql-statements">
757 <title>Basic Statements</title>
760 In this section and the following ones, we describe all the statement
761 types that are explicitly understood by
762 <application>PL/pgSQL</application>.
763 Anything not recognized as one of these statement types is presumed
764 to be an SQL command and is sent to the main database engine to execute,
765 as described in <xref linkend="plpgsql-statements-sql-noresult">
766 and <xref linkend="plpgsql-statements-sql-onerow">.
769 <sect2 id="plpgsql-statements-assignment">
770 <title>Assignment</title>
773 An assignment of a value to a <application>PL/pgSQL</application>
774 variable is written as:
776 <replaceable>variable</replaceable> := <replaceable>expression</replaceable>;
778 As explained previously, the expression in such a statement is evaluated
779 by means of an SQL <command>SELECT</> command sent to the main
780 database engine. The expression must yield a single value (possibly
781 a row value, if the variable is a row or record variable). The target
782 variable can be a simple variable (optionally qualified with a block
783 name), a field of a row or record variable, or an element of an array
784 that is a simple variable or field.
788 If the expression's result data type doesn't match the variable's
789 data type, or the variable has a specific size/precision
790 (like <type>char(20)</type>), the result value will be implicitly
791 converted by the <application>PL/pgSQL</application> interpreter using
792 the result type's output-function and
793 the variable type's input-function. Note that this could potentially
794 result in run-time errors generated by the input function, if the
795 string form of the result value is not acceptable to the input function.
801 tax := subtotal * 0.06;
802 my_record.user_id := 20;
807 <sect2 id="plpgsql-statements-sql-noresult">
808 <title>Executing a Command With No Result</title>
811 For any SQL command that does not return rows, for example
812 <command>INSERT</> without a <literal>RETURNING</> clause, you can
813 execute the command within a <application>PL/pgSQL</application> function
814 just by writing the command.
818 Any <application>PL/pgSQL</application> variable name appearing
819 in the command text is treated as a parameter, and then the
820 current value of the variable is provided as the parameter value
821 at run time. This is exactly like the processing described earlier
822 for expressions; for details see <xref linkend="plpgsql-var-subst">.
826 When executing a SQL command in this way,
827 <application>PL/pgSQL</application> plans the command just once
828 and re-uses the plan on subsequent executions, for the life of
829 the database connection. The implications of this are discussed
830 in detail in <xref linkend="plpgsql-plan-caching">.
834 Sometimes it is useful to evaluate an expression or <command>SELECT</>
835 query but discard the result, for example when calling a function
836 that has side-effects but no useful result value. To do
837 this in <application>PL/pgSQL</application>, use the
838 <command>PERFORM</command> statement:
841 PERFORM <replaceable>query</replaceable>;
844 This executes <replaceable>query</replaceable> and discards the
845 result. Write the <replaceable>query</replaceable> the same
846 way you would write an SQL <command>SELECT</> command, but replace the
847 initial keyword <command>SELECT</> with <command>PERFORM</command>.
848 <application>PL/pgSQL</application> variables will be
849 substituted into the query just as for commands that return no result,
850 and the plan is cached in the same way. Also, the special variable
851 <literal>FOUND</literal> is set to true if the query produced at
852 least one row, or false if it produced no rows (see
853 <xref linkend="plpgsql-statements-diagnostics">).
858 One might expect that writing <command>SELECT</command> directly
859 would accomplish this result, but at
860 present the only accepted way to do it is
861 <command>PERFORM</command>. A SQL command that can return rows,
862 such as <command>SELECT</command>, will be rejected as an error
863 unless it has an <literal>INTO</> clause as discussed in the
871 PERFORM create_mv('cs_session_page_requests_mv', my_query);
876 <sect2 id="plpgsql-statements-sql-onerow">
877 <title>Executing a Query with a Single-Row Result</title>
879 <indexterm zone="plpgsql-statements-sql-onerow">
880 <primary>SELECT INTO</primary>
881 <secondary>in PL/pgSQL</secondary>
884 <indexterm zone="plpgsql-statements-sql-onerow">
885 <primary>RETURNING INTO</primary>
886 <secondary>in PL/pgSQL</secondary>
890 The result of a SQL command yielding a single row (possibly of multiple
891 columns) can be assigned to a record variable, row-type variable, or list
892 of scalar variables. This is done by writing the base SQL command and
893 adding an <literal>INTO</> clause. For example,
896 SELECT <replaceable>select_expressions</replaceable> INTO <optional>STRICT</optional> <replaceable>target</replaceable> FROM ...;
897 INSERT ... RETURNING <replaceable>expressions</replaceable> INTO <optional>STRICT</optional> <replaceable>target</replaceable>;
898 UPDATE ... RETURNING <replaceable>expressions</replaceable> INTO <optional>STRICT</optional> <replaceable>target</replaceable>;
899 DELETE ... RETURNING <replaceable>expressions</replaceable> INTO <optional>STRICT</optional> <replaceable>target</replaceable>;
902 where <replaceable>target</replaceable> can be a record variable, a row
903 variable, or a comma-separated list of simple variables and
905 <application>PL/pgSQL</application> variables will be
906 substituted into the rest of the query, and the plan is cached,
907 just as described above for commands that do not return rows.
908 This works for <command>SELECT</>,
909 <command>INSERT</>/<command>UPDATE</>/<command>DELETE</> with
910 <literal>RETURNING</>, and utility commands that return row-set
911 results (such as <command>EXPLAIN</>).
912 Except for the <literal>INTO</> clause, the SQL command is the same
913 as it would be written outside <application>PL/pgSQL</application>.
918 Note that this interpretation of <command>SELECT</> with <literal>INTO</>
919 is quite different from <productname>PostgreSQL</>'s regular
920 <command>SELECT INTO</command> command, wherein the <literal>INTO</>
921 target is a newly created table. If you want to create a table from a
922 <command>SELECT</> result inside a
923 <application>PL/pgSQL</application> function, use the syntax
924 <command>CREATE TABLE ... AS SELECT</command>.
929 If a row or a variable list is used as target, the query's result columns
930 must exactly match the structure of the target as to number and data
931 types, or else a run-time error
932 occurs. When a record variable is the target, it automatically
933 configures itself to the row type of the query result columns.
937 The <literal>INTO</> clause can appear almost anywhere in the SQL
938 command. Customarily it is written either just before or just after
939 the list of <replaceable>select_expressions</replaceable> in a
940 <command>SELECT</> command, or at the end of the command for other
941 command types. It is recommended that you follow this convention
942 in case the <application>PL/pgSQL</application> parser becomes
943 stricter in future versions.
947 If <literal>STRICT</literal> is not specified in the <literal>INTO</>
948 clause, then <replaceable>target</replaceable> will be set to the first
949 row returned by the query, or to nulls if the query returned no rows.
950 (Note that <quote>the first row</> is not
951 well-defined unless you've used <literal>ORDER BY</>.) Any result rows
952 after the first row are discarded.
953 You can check the special <literal>FOUND</literal> variable (see
954 <xref linkend="plpgsql-statements-diagnostics">) to
955 determine whether a row was returned:
958 SELECT * INTO myrec FROM emp WHERE empname = myname;
960 RAISE EXCEPTION 'employee % not found', myname;
964 If the <literal>STRICT</literal> option is specified, the query must
965 return exactly one row or a run-time error will be reported, either
966 <literal>NO_DATA_FOUND</> (no rows) or <literal>TOO_MANY_ROWS</>
967 (more than one row). You can use an exception block if you wish
968 to catch the error, for example:
972 SELECT * INTO STRICT myrec FROM emp WHERE empname = myname;
974 WHEN NO_DATA_FOUND THEN
975 RAISE EXCEPTION 'employee % not found', myname;
976 WHEN TOO_MANY_ROWS THEN
977 RAISE EXCEPTION 'employee % not unique', myname;
980 Successful execution of a command with <literal>STRICT</>
981 always sets <literal>FOUND</literal> to true.
985 For <command>INSERT</>/<command>UPDATE</>/<command>DELETE</> with
986 <literal>RETURNING</>, <application>PL/pgSQL</application> reports
987 an error for more than one returned row, even when
988 <literal>STRICT</literal> is not specified. This is because there
989 is no option such as <literal>ORDER BY</> with which to determine
990 which affected row should be returned.
995 The <literal>STRICT</> option matches the behavior of
996 Oracle PL/SQL's <command>SELECT INTO</command> and related statements.
1001 To handle cases where you need to process multiple result rows
1002 from a SQL query, see <xref linkend="plpgsql-records-iterating">.
1007 <sect2 id="plpgsql-statements-executing-dyn">
1008 <title>Executing Dynamic Commands</title>
1011 Oftentimes you will want to generate dynamic commands inside your
1012 <application>PL/pgSQL</application> functions, that is, commands
1013 that will involve different tables or different data types each
1014 time they are executed. <application>PL/pgSQL</application>'s
1015 normal attempts to cache plans for commands (as discussed in
1016 <xref linkend="plpgsql-plan-caching">) will not work in such
1017 scenarios. To handle this sort of problem, the
1018 <command>EXECUTE</command> statement is provided:
1021 EXECUTE <replaceable class="command">command-string</replaceable> <optional> INTO <optional>STRICT</optional> <replaceable>target</replaceable> </optional> <optional> USING <replaceable>expression</replaceable> <optional>, ... </optional> </optional>;
1024 where <replaceable>command-string</replaceable> is an expression
1025 yielding a string (of type <type>text</type>) containing the
1026 command to be executed. The optional <replaceable>target</replaceable>
1027 is a record variable, a row variable, or a comma-separated list of
1028 simple variables and record/row fields, into which the results of
1029 the command will be stored. The optional <literal>USING</> expressions
1030 supply values to be inserted into the command.
1034 No substitution of <application>PL/pgSQL</> variables is done on the
1035 computed command string. Any required variable values must be inserted
1036 in the command string as it is constructed; or you can use parameters
1041 Also, there is no plan caching for commands executed via
1042 <command>EXECUTE</command>. Instead, the
1043 command is prepared each time the statement is run. Thus the command
1044 string can be dynamically created within the function to perform
1045 actions on different tables and columns.
1049 The <literal>INTO</literal> clause specifies where the results of
1050 a SQL command returning rows should be assigned. If a row
1051 or variable list is provided, it must exactly match the structure
1052 of the query's results (when a
1053 record variable is used, it will configure itself to match the
1054 result structure automatically). If multiple rows are returned,
1055 only the first will be assigned to the <literal>INTO</literal>
1056 variable. If no rows are returned, NULL is assigned to the
1057 <literal>INTO</literal> variable(s). If no <literal>INTO</literal>
1058 clause is specified, the query results are discarded.
1062 If the <literal>STRICT</> option is given, an error is reported
1063 unless the query produces exactly one row.
1067 The command string can use parameter values, which are referenced
1068 in the command as <literal>$1</>, <literal>$2</>, etc.
1069 These symbols refer to values supplied in the <literal>USING</>
1070 clause. This method is often preferable to inserting data values
1071 into the command string as text: it avoids run-time overhead of
1072 converting the values to text and back, and it is much less prone
1073 to SQL-injection attacks since there is no need for quoting or escaping.
1076 EXECUTE 'SELECT count(*) FROM mytable WHERE inserted_by = $1 AND inserted <= $2'
1078 USING checked_user, checked_date;
1083 Note that parameter symbols can only be used for data values
1084 — if you want to use dynamically determined table or column
1085 names, you must insert them into the command string textually.
1086 For example, if the preceding query needed to be done against a
1087 dynamically selected table, you could do this:
1089 EXECUTE 'SELECT count(*) FROM '
1090 || tabname::regclass
1091 || ' WHERE inserted_by = $1 AND inserted <= $2'
1093 USING checked_user, checked_date;
1095 Another restriction on parameter symbols is that they only work in
1096 <command>SELECT</>, <command>INSERT</>, <command>UPDATE</>, and
1097 <command>DELETE</> commands. In other statement
1098 types (generically called utility statements), you must insert
1099 values textually even if they are just data values.
1103 An <command>EXECUTE</> with a simple constant command string and some
1104 <literal>USING</> parameters, as in the first example above, is
1105 functionally equivalent to just writing the command directly in
1106 <application>PL/pgSQL</application> and allowing replacement of
1107 <application>PL/pgSQL</application> variables to happen automatically.
1108 The important difference is that <command>EXECUTE</> will re-plan
1109 the command on each execution, generating a plan that is specific
1110 to the current parameter values; whereas
1111 <application>PL/pgSQL</application> normally creates a generic plan
1112 and caches it for re-use. In situations where the best plan depends
1113 strongly on the parameter values, <command>EXECUTE</> can be
1114 significantly faster; while when the plan is not sensitive to parameter
1115 values, re-planning will be a waste.
1119 <command>SELECT INTO</command> is not currently supported within
1120 <command>EXECUTE</command>; instead, execute a plain <command>SELECT</>
1121 command and specify <literal>INTO</> as part of the <command>EXECUTE</>
1127 The <application>PL/pgSQL</application>
1128 <command>EXECUTE</command> statement is not related to the
1129 <xref linkend="sql-execute"> SQL
1130 statement supported by the
1131 <productname>PostgreSQL</productname> server. The server's
1132 <command>EXECUTE</command> statement cannot be used directly within
1133 <application>PL/pgSQL</> functions (and is not needed).
1137 <example id="plpgsql-quote-literal-example">
1138 <title>Quoting values in dynamic queries</title>
1141 <primary>quote_ident</primary>
1142 <secondary>use in PL/PgSQL</secondary>
1146 <primary>quote_literal</primary>
1147 <secondary>use in PL/PgSQL</secondary>
1151 <primary>quote_nullable</primary>
1152 <secondary>use in PL/PgSQL</secondary>
1156 When working with dynamic commands you will often have to handle escaping
1157 of single quotes. The recommended method for quoting fixed text in your
1158 function body is dollar quoting. (If you have legacy code that does
1159 not use dollar quoting, please refer to the
1160 overview in <xref linkend="plpgsql-quote-tips">, which can save you
1161 some effort when translating said code to a more reasonable scheme.)
1165 Dynamic values that are to be inserted into the constructed
1166 query require careful handling since they might themselves contain
1168 An example (this assumes that you are using dollar quoting for the
1169 function as a whole, so the quote marks need not be doubled):
1171 EXECUTE 'UPDATE tbl SET '
1172 || quote_ident(colname)
1174 || quote_literal(newvalue)
1176 || quote_literal(keyvalue);
1181 This example demonstrates the use of the
1182 <function>quote_ident</function> and
1183 <function>quote_literal</function> functions (see <xref
1184 linkend="functions-string">). For safety, expressions containing column
1185 or table identifiers should be passed through
1186 <function>quote_ident</function> before insertion in a dynamic query.
1187 Expressions containing values that should be literal strings in the
1188 constructed command should be passed through <function>quote_literal</>.
1189 These functions take the appropriate steps to return the input text
1190 enclosed in double or single quotes respectively, with any embedded
1191 special characters properly escaped.
1195 Because <function>quote_literal</function> is labelled
1196 <literal>STRICT</literal>, it will always return null when called with a
1197 null argument. In the above example, if <literal>newvalue</> or
1198 <literal>keyvalue</> were null, the entire dynamic query string would
1199 become null, leading to an error from <command>EXECUTE</command>.
1200 You can avoid this problem by using the <function>quote_nullable</>
1201 function, which works the same as <function>quote_literal</> except that
1202 when called with a null argument it returns the string <literal>NULL</>.
1205 EXECUTE 'UPDATE tbl SET '
1206 || quote_ident(colname)
1208 || quote_nullable(newvalue)
1210 || quote_nullable(keyvalue);
1212 If you are dealing with values that might be null, you should usually
1213 use <function>quote_nullable</> in place of <function>quote_literal</>.
1217 As always, care must be taken to ensure that null values in a query do
1218 not deliver unintended results. For example the <literal>WHERE</> clause
1220 'WHERE key = ' || quote_nullable(keyvalue)
1222 will never succeed if <literal>keyvalue</> is null, because the
1223 result of using the equality operator <literal>=</> with a null operand
1224 is always null. If you wish null to work like an ordinary key value,
1225 you would need to rewrite the above as
1227 'WHERE key IS NOT DISTINCT FROM ' || quote_nullable(keyvalue)
1229 (At present, <literal>IS NOT DISTINCT FROM</> is handled much less
1230 efficiently than <literal>=</>, so don't do this unless you must.
1231 See <xref linkend="functions-comparison"> for
1232 more information on nulls and <literal>IS DISTINCT</>.)
1236 Note that dollar quoting is only useful for quoting fixed text.
1237 It would be a very bad idea to try to write this example as:
1239 EXECUTE 'UPDATE tbl SET '
1240 || quote_ident(colname)
1243 || '$$ WHERE key = '
1244 || quote_literal(keyvalue);
1246 because it would break if the contents of <literal>newvalue</>
1247 happened to contain <literal>$$</>. The same objection would
1248 apply to any other dollar-quoting delimiter you might pick.
1249 So, to safely quote text that is not known in advance, you
1250 <emphasis>must</> use <function>quote_literal</>,
1251 <function>quote_nullable</>, or <function>quote_ident</>, as appropriate.
1256 A much larger example of a dynamic command and
1257 <command>EXECUTE</command> can be seen in <xref
1258 linkend="plpgsql-porting-ex2">, which builds and executes a
1259 <command>CREATE FUNCTION</> command to define a new function.
1263 <sect2 id="plpgsql-statements-diagnostics">
1264 <title>Obtaining the Result Status</title>
1267 There are several ways to determine the effect of a command. The
1268 first method is to use the <command>GET DIAGNOSTICS</command>
1269 command, which has the form:
1272 GET DIAGNOSTICS <replaceable>variable</replaceable> = <replaceable>item</replaceable> <optional> , ... </optional>;
1275 This command allows retrieval of system status indicators. Each
1276 <replaceable>item</replaceable> is a key word identifying a state
1277 value to be assigned to the specified variable (which should be
1278 of the right data type to receive it). The currently available
1279 status items are <varname>ROW_COUNT</>, the number of rows
1280 processed by the last <acronym>SQL</acronym> command sent to
1281 the <acronym>SQL</acronym> engine, and <varname>RESULT_OID</>,
1282 the OID of the last row inserted by the most recent
1283 <acronym>SQL</acronym> command. Note that <varname>RESULT_OID</>
1284 is only useful after an <command>INSERT</command> command into a
1285 table containing OIDs.
1291 GET DIAGNOSTICS integer_var = ROW_COUNT;
1296 The second method to determine the effects of a command is to check the
1297 special variable named <literal>FOUND</literal>, which is of
1298 type <type>boolean</type>. <literal>FOUND</literal> starts out
1299 false within each <application>PL/pgSQL</application> function call.
1300 It is set by each of the following types of statements:
1305 A <command>SELECT INTO</command> statement sets
1306 <literal>FOUND</literal> true if a row is assigned, false if no
1312 A <command>PERFORM</> statement sets <literal>FOUND</literal>
1313 true if it produces (and discards) one or more rows, false if
1319 <command>UPDATE</>, <command>INSERT</>, and <command>DELETE</>
1320 statements set <literal>FOUND</literal> true if at least one
1321 row is affected, false if no row is affected.
1326 A <command>FETCH</> statement sets <literal>FOUND</literal>
1327 true if it returns a row, false if no row is returned.
1332 A <command>MOVE</> statement sets <literal>FOUND</literal>
1333 true if it successfully repositions the cursor, false otherwise.
1339 A <command>FOR</> statement sets <literal>FOUND</literal> true
1340 if it iterates one or more times, else false. This applies to
1341 all four variants of the <command>FOR</> statement (integer
1342 <command>FOR</> loops, record-set <command>FOR</> loops,
1343 dynamic record-set <command>FOR</> loops, and cursor
1344 <command>FOR</> loops).
1345 <literal>FOUND</literal> is set this way when the
1346 <command>FOR</> loop exits; inside the execution of the loop,
1347 <literal>FOUND</literal> is not modified by the
1348 <command>FOR</> statement, although it might be changed by the
1349 execution of other statements within the loop body.
1354 <command>RETURN QUERY</command> and <command>RETURN QUERY
1355 EXECUTE</command> statements set <literal>FOUND</literal>
1356 true if the query returns at least one row, false if no row
1362 Other <application>PL/pgSQL</application> statements do not change
1363 the state of <literal>FOUND</literal>.
1364 Note in particular that <command>EXECUTE</command>
1365 changes the output of <command>GET DIAGNOSTICS</command>, but
1366 does not change <literal>FOUND</literal>.
1370 <literal>FOUND</literal> is a local variable within each
1371 <application>PL/pgSQL</application> function; any changes to it
1372 affect only the current function.
1377 <sect2 id="plpgsql-statements-null">
1378 <title>Doing Nothing At All</title>
1381 Sometimes a placeholder statement that does nothing is useful.
1382 For example, it can indicate that one arm of an if/then/else
1383 chain is deliberately empty. For this purpose, use the
1384 <command>NULL</command> statement:
1392 For example, the following two fragments of code are equivalent:
1397 WHEN division_by_zero THEN
1398 NULL; -- ignore the error
1406 WHEN division_by_zero THEN -- ignore the error
1409 Which is preferable is a matter of taste.
1414 In Oracle's PL/SQL, empty statement lists are not allowed, and so
1415 <command>NULL</> statements are <emphasis>required</> for situations
1416 such as this. <application>PL/pgSQL</application> allows you to
1417 just write nothing, instead.
1424 <sect1 id="plpgsql-control-structures">
1425 <title>Control Structures</title>
1428 Control structures are probably the most useful (and
1429 important) part of <application>PL/pgSQL</>. With
1430 <application>PL/pgSQL</>'s control structures,
1431 you can manipulate <productname>PostgreSQL</> data in a very
1432 flexible and powerful way.
1435 <sect2 id="plpgsql-statements-returning">
1436 <title>Returning From a Function</title>
1439 There are two commands available that allow you to return data
1440 from a function: <command>RETURN</command> and <command>RETURN
1445 <title><command>RETURN</></title>
1448 RETURN <replaceable>expression</replaceable>;
1452 <command>RETURN</command> with an expression terminates the
1453 function and returns the value of
1454 <replaceable>expression</replaceable> to the caller. This form
1455 is used for <application>PL/pgSQL</> functions that do
1460 When returning a scalar type, any expression can be used. The
1461 expression's result will be automatically cast into the
1462 function's return type as described for assignments. To return a
1463 composite (row) value, you must write a record or row variable
1464 as the <replaceable>expression</replaceable>.
1468 If you declared the function with output parameters, write just
1469 <command>RETURN</command> with no expression. The current values
1470 of the output parameter variables will be returned.
1474 If you declared the function to return <type>void</type>, a
1475 <command>RETURN</command> statement can be used to exit the function
1476 early; but do not write an expression following
1477 <command>RETURN</command>.
1481 The return value of a function cannot be left undefined. If
1482 control reaches the end of the top-level block of the function
1483 without hitting a <command>RETURN</command> statement, a run-time
1484 error will occur. This restriction does not apply to functions
1485 with output parameters and functions returning <type>void</type>,
1486 however. In those cases a <command>RETURN</command> statement is
1487 automatically executed if the top-level block finishes.
1492 <title><command>RETURN NEXT</> and <command>RETURN QUERY</command></title>
1494 <primary>RETURN NEXT</primary>
1495 <secondary>in PL/PgSQL</secondary>
1498 <primary>RETURN QUERY</primary>
1499 <secondary>in PL/PgSQL</secondary>
1503 RETURN NEXT <replaceable>expression</replaceable>;
1504 RETURN QUERY <replaceable>query</replaceable>;
1505 RETURN QUERY EXECUTE <replaceable class="command">command-string</replaceable> <optional> USING <replaceable>expression</replaceable> <optional>, ... </optional> </optional>;
1509 When a <application>PL/pgSQL</> function is declared to return
1510 <literal>SETOF <replaceable>sometype</></literal>, the procedure
1511 to follow is slightly different. In that case, the individual
1512 items to return are specified by a sequence of <command>RETURN
1513 NEXT</command> or <command>RETURN QUERY</command> commands, and
1514 then a final <command>RETURN</command> command with no argument
1515 is used to indicate that the function has finished executing.
1516 <command>RETURN NEXT</command> can be used with both scalar and
1517 composite data types; with a composite result type, an entire
1518 <quote>table</quote> of results will be returned.
1519 <command>RETURN QUERY</command> appends the results of executing
1520 a query to the function's result set. <command>RETURN
1521 NEXT</command> and <command>RETURN QUERY</command> can be freely
1522 intermixed in a single set-returning function, in which case
1523 their results will be concatenated.
1527 <command>RETURN NEXT</command> and <command>RETURN
1528 QUERY</command> do not actually return from the function —
1529 they simply append zero or more rows to the function's result
1530 set. Execution then continues with the next statement in the
1531 <application>PL/pgSQL</> function. As successive
1532 <command>RETURN NEXT</command> or <command>RETURN
1533 QUERY</command> commands are executed, the result set is built
1534 up. A final <command>RETURN</command>, which should have no
1535 argument, causes control to exit the function (or you can just
1536 let control reach the end of the function).
1540 <command>RETURN QUERY</command> has a variant
1541 <command>RETURN QUERY EXECUTE</command>, which specifies the
1542 query to be executed dynamically. Parameter expressions can
1543 be inserted into the computed query string via <literal>USING</>,
1544 in just the same way as in the <command>EXECUTE</> command.
1548 If you declared the function with output parameters, write just
1549 <command>RETURN NEXT</command> with no expression. On each
1550 execution, the current values of the output parameter
1551 variable(s) will be saved for eventual return as a row of the
1552 result. Note that you must declare the function as returning
1553 <literal>SETOF record</literal> when there are multiple output
1554 parameters, or <literal>SETOF <replaceable>sometype</></literal>
1555 when there is just one output parameter of type
1556 <replaceable>sometype</>, in order to create a set-returning
1557 function with output parameters.
1561 Here is an example of a function using <command>RETURN
1565 CREATE TABLE foo (fooid INT, foosubid INT, fooname TEXT);
1566 INSERT INTO foo VALUES (1, 2, 'three');
1567 INSERT INTO foo VALUES (4, 5, 'six');
1569 CREATE OR REPLACE FUNCTION getAllFoo() RETURNS SETOF foo AS
1574 FOR r IN SELECT * FROM foo
1577 -- can do some processing here
1578 RETURN NEXT r; -- return current row of SELECT
1583 LANGUAGE 'plpgsql' ;
1585 SELECT * FROM getallfoo();
1591 The current implementation of <command>RETURN NEXT</command>
1592 and <command>RETURN QUERY</command> stores the entire result set
1593 before returning from the function, as discussed above. That
1594 means that if a <application>PL/pgSQL</> function produces a
1595 very large result set, performance might be poor: data will be
1596 written to disk to avoid memory exhaustion, but the function
1597 itself will not return until the entire result set has been
1598 generated. A future version of <application>PL/pgSQL</> might
1599 allow users to define set-returning functions
1600 that do not have this limitation. Currently, the point at
1601 which data begins being written to disk is controlled by the
1602 <xref linkend="guc-work-mem">
1603 configuration variable. Administrators who have sufficient
1604 memory to store larger result sets in memory should consider
1605 increasing this parameter.
1611 <sect2 id="plpgsql-conditionals">
1612 <title>Conditionals</title>
1615 <command>IF</> and <command>CASE</> statements let you execute
1616 alternative commands based on certain conditions.
1617 <application>PL/pgSQL</> has three forms of <command>IF</>:
1620 <para><literal>IF ... THEN</></>
1623 <para><literal>IF ... THEN ... ELSE</></>
1626 <para><literal>IF ... THEN ... ELSIF ... THEN ... ELSE</></>
1630 and two forms of <command>CASE</>:
1633 <para><literal>CASE ... WHEN ... THEN ... ELSE ... END CASE</></>
1636 <para><literal>CASE WHEN ... THEN ... ELSE ... END CASE</></>
1642 <title><literal>IF-THEN</></title>
1645 IF <replaceable>boolean-expression</replaceable> THEN
1646 <replaceable>statements</replaceable>
1651 <literal>IF-THEN</literal> statements are the simplest form of
1652 <literal>IF</literal>. The statements between
1653 <literal>THEN</literal> and <literal>END IF</literal> will be
1654 executed if the condition is true. Otherwise, they are
1661 IF v_user_id <> 0 THEN
1662 UPDATE users SET email = v_email WHERE user_id = v_user_id;
1669 <title><literal>IF-THEN-ELSE</></title>
1672 IF <replaceable>boolean-expression</replaceable> THEN
1673 <replaceable>statements</replaceable>
1675 <replaceable>statements</replaceable>
1680 <literal>IF-THEN-ELSE</literal> statements add to
1681 <literal>IF-THEN</literal> by letting you specify an
1682 alternative set of statements that should be executed if the
1683 condition is not true. (Note this includes the case where the
1684 condition evaluates to NULL.)
1690 IF parentid IS NULL OR parentid = ''
1694 RETURN hp_true_filename(parentid) || '/' || fullname;
1699 IF v_count > 0 THEN
1700 INSERT INTO users_count (count) VALUES (v_count);
1710 <title><literal>IF-THEN-ELSIF</></title>
1713 IF <replaceable>boolean-expression</replaceable> THEN
1714 <replaceable>statements</replaceable>
1715 <optional> ELSIF <replaceable>boolean-expression</replaceable> THEN
1716 <replaceable>statements</replaceable>
1717 <optional> ELSIF <replaceable>boolean-expression</replaceable> THEN
1718 <replaceable>statements</replaceable>
1723 <replaceable>statements</replaceable> </optional>
1728 Sometimes there are more than just two alternatives.
1729 <literal>IF-THEN-ELSIF</> provides a convenient
1730 method of checking several alternatives in turn.
1731 The <literal>IF</> conditions are tested successively
1732 until the first one that is true is found. Then the
1733 associated statement(s) are executed, after which control
1734 passes to the next statement after <literal>END IF</>.
1735 (Any subsequent <literal>IF</> conditions are <emphasis>not</>
1736 tested.) If none of the <literal>IF</> conditions is true,
1737 then the <literal>ELSE</> block (if any) is executed.
1746 ELSIF number > 0 THEN
1747 result := 'positive';
1748 ELSIF number < 0 THEN
1749 result := 'negative';
1751 -- hmm, the only other possibility is that number is null
1758 The key word <literal>ELSIF</> can also be spelled
1763 An alternative way of accomplishing the same task is to nest
1764 <literal>IF-THEN-ELSE</literal> statements, as in the
1768 IF demo_row.sex = 'm' THEN
1769 pretty_sex := 'man';
1771 IF demo_row.sex = 'f' THEN
1772 pretty_sex := 'woman';
1779 However, this method requires writing a matching <literal>END IF</>
1780 for each <literal>IF</>, so it is much more cumbersome than
1781 using <literal>ELSIF</> when there are many alternatives.
1786 <title>Simple <literal>CASE</></title>
1789 CASE <replaceable>search-expression</replaceable>
1790 WHEN <replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> <optional> ... </optional></optional> THEN
1791 <replaceable>statements</replaceable>
1792 <optional> WHEN <replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> <optional> ... </optional></optional> THEN
1793 <replaceable>statements</replaceable>
1796 <replaceable>statements</replaceable> </optional>
1801 The simple form of <command>CASE</> provides conditional execution
1802 based on equality of operands. The <replaceable>search-expression</>
1803 is evaluated (once) and successively compared to each
1804 <replaceable>expression</> in the <literal>WHEN</> clauses.
1805 If a match is found, then the corresponding
1806 <replaceable>statements</replaceable> are executed, and then control
1807 passes to the next statement after <literal>END CASE</>. (Subsequent
1808 <literal>WHEN</> expressions are not evaluated.) If no match is
1809 found, the <literal>ELSE</> <replaceable>statements</replaceable> are
1810 executed; but if <literal>ELSE</> is not present, then a
1811 <literal>CASE_NOT_FOUND</literal> exception is raised.
1815 Here is a simple example:
1820 msg := 'one or two';
1822 msg := 'other value than one or two';
1829 <title>Searched <literal>CASE</></title>
1833 WHEN <replaceable>boolean-expression</replaceable> THEN
1834 <replaceable>statements</replaceable>
1835 <optional> WHEN <replaceable>boolean-expression</replaceable> THEN
1836 <replaceable>statements</replaceable>
1839 <replaceable>statements</replaceable> </optional>
1844 The searched form of <command>CASE</> provides conditional execution
1845 based on truth of Boolean expressions. Each <literal>WHEN</> clause's
1846 <replaceable>boolean-expression</replaceable> is evaluated in turn,
1847 until one is found that yields <literal>true</>. Then the
1848 corresponding <replaceable>statements</replaceable> are executed, and
1849 then control passes to the next statement after <literal>END CASE</>.
1850 (Subsequent <literal>WHEN</> expressions are not evaluated.)
1851 If no true result is found, the <literal>ELSE</>
1852 <replaceable>statements</replaceable> are executed;
1853 but if <literal>ELSE</> is not present, then a
1854 <literal>CASE_NOT_FOUND</literal> exception is raised.
1862 WHEN x BETWEEN 0 AND 10 THEN
1863 msg := 'value is between zero and ten';
1864 WHEN x BETWEEN 11 AND 20 THEN
1865 msg := 'value is between eleven and twenty';
1871 This form of <command>CASE</> is entirely equivalent to
1872 <literal>IF-THEN-ELSIF</>, except for the rule that reaching
1873 an omitted <literal>ELSE</> clause results in an error rather
1880 <sect2 id="plpgsql-control-structures-loops">
1881 <title>Simple Loops</title>
1883 <indexterm zone="plpgsql-control-structures-loops">
1884 <primary>loop</primary>
1885 <secondary>in PL/pgSQL</secondary>
1889 With the <literal>LOOP</>, <literal>EXIT</>,
1890 <literal>CONTINUE</>, <literal>WHILE</>, and <literal>FOR</>
1891 statements, you can arrange for your <application>PL/pgSQL</>
1892 function to repeat a series of commands.
1896 <title><literal>LOOP</></title>
1899 <optional> <<<replaceable>label</replaceable>>> </optional>
1901 <replaceable>statements</replaceable>
1902 END LOOP <optional> <replaceable>label</replaceable> </optional>;
1906 <literal>LOOP</> defines an unconditional loop that is repeated
1907 indefinitely until terminated by an <literal>EXIT</> or
1908 <command>RETURN</command> statement. The optional
1909 <replaceable>label</replaceable> can be used by <literal>EXIT</>
1910 and <literal>CONTINUE</literal> statements within nested loops to
1911 specify which loop those statements refer to.
1916 <title><literal>EXIT</></title>
1919 <primary>EXIT</primary>
1920 <secondary>in PL/pgSQL</secondary>
1924 EXIT <optional> <replaceable>label</replaceable> </optional> <optional> WHEN <replaceable>boolean-expression</replaceable> </optional>;
1928 If no <replaceable>label</replaceable> is given, the innermost
1929 loop is terminated and the statement following <literal>END
1930 LOOP</> is executed next. If <replaceable>label</replaceable>
1931 is given, it must be the label of the current or some outer
1932 level of nested loop or block. Then the named loop or block is
1933 terminated and control continues with the statement after the
1934 loop's/block's corresponding <literal>END</>.
1938 If <literal>WHEN</> is specified, the loop exit occurs only if
1939 <replaceable>boolean-expression</> is true. Otherwise, control passes
1940 to the statement after <literal>EXIT</>.
1944 <literal>EXIT</> can be used with all types of loops; it is
1945 not limited to use with unconditional loops.
1950 <literal>BEGIN</literal> block, <literal>EXIT</literal> passes
1951 control to the next statement after the end of the block.
1952 Note that a label must be used for this purpose; an unlabelled
1953 <literal>EXIT</literal> is never considered to match a
1954 <literal>BEGIN</literal> block. (This is a change from
1955 pre-8.4 releases of <productname>PostgreSQL</productname>, which
1956 would allow an unlabelled <literal>EXIT</literal> to match
1957 a <literal>BEGIN</literal> block.)
1964 -- some computations
1965 IF count > 0 THEN
1971 -- some computations
1972 EXIT WHEN count > 0; -- same result as previous example
1975 <<ablock>>
1977 -- some computations
1978 IF stocks > 100000 THEN
1979 EXIT ablock; -- causes exit from the BEGIN block
1981 -- computations here will be skipped when stocks > 100000
1988 <title><literal>CONTINUE</></title>
1991 <primary>CONTINUE</primary>
1992 <secondary>in PL/pgSQL</secondary>
1996 CONTINUE <optional> <replaceable>label</replaceable> </optional> <optional> WHEN <replaceable>boolean-expression</replaceable> </optional>;
2000 If no <replaceable>label</> is given, the next iteration of
2001 the innermost loop is begun. That is, all statements remaining
2002 in the loop body are skipped, and control returns
2003 to the loop control expression (if any) to determine whether
2004 another loop iteration is needed.
2005 If <replaceable>label</> is present, it
2006 specifies the label of the loop whose execution will be
2011 If <literal>WHEN</> is specified, the next iteration of the
2012 loop is begun only if <replaceable>boolean-expression</> is
2013 true. Otherwise, control passes to the statement after
2014 <literal>CONTINUE</>.
2018 <literal>CONTINUE</> can be used with all types of loops; it
2019 is not limited to use with unconditional loops.
2026 -- some computations
2027 EXIT WHEN count > 100;
2028 CONTINUE WHEN count < 50;
2029 -- some computations for count IN [50 .. 100]
2037 <title><literal>WHILE</></title>
2040 <primary>WHILE</primary>
2041 <secondary>in PL/pgSQL</secondary>
2045 <optional> <<<replaceable>label</replaceable>>> </optional>
2046 WHILE <replaceable>boolean-expression</replaceable> LOOP
2047 <replaceable>statements</replaceable>
2048 END LOOP <optional> <replaceable>label</replaceable> </optional>;
2052 The <literal>WHILE</> statement repeats a
2053 sequence of statements so long as the
2054 <replaceable>boolean-expression</replaceable>
2055 evaluates to true. The expression is checked just before
2056 each entry to the loop body.
2062 WHILE amount_owed > 0 AND gift_certificate_balance > 0 LOOP
2063 -- some computations here
2067 -- some computations here
2073 <sect3 id="plpgsql-integer-for">
2074 <title><literal>FOR</> (integer variant)</title>
2077 <optional> <<<replaceable>label</replaceable>>> </optional>
2078 FOR <replaceable>name</replaceable> IN <optional> REVERSE </optional> <replaceable>expression</replaceable> .. <replaceable>expression</replaceable> <optional> BY <replaceable>expression</replaceable> </optional> LOOP
2079 <replaceable>statements</replaceable>
2080 END LOOP <optional> <replaceable>label</replaceable> </optional>;
2084 This form of <literal>FOR</> creates a loop that iterates over a range
2085 of integer values. The variable
2086 <replaceable>name</replaceable> is automatically defined as type
2087 <type>integer</> and exists only inside the loop (any existing
2088 definition of the variable name is ignored within the loop).
2089 The two expressions giving
2090 the lower and upper bound of the range are evaluated once when entering
2091 the loop. If the <literal>BY</> clause isn't specified the iteration
2092 step is 1, otherwise it's the value specified in the <literal>BY</>
2093 clause, which again is evaluated once on loop entry.
2094 If <literal>REVERSE</> is specified then the step value is
2095 subtracted, rather than added, after each iteration.
2099 Some examples of integer <literal>FOR</> loops:
2102 -- i will take on the values 1,2,3,4,5,6,7,8,9,10 within the loop
2105 FOR i IN REVERSE 10..1 LOOP
2106 -- i will take on the values 10,9,8,7,6,5,4,3,2,1 within the loop
2109 FOR i IN REVERSE 10..1 BY 2 LOOP
2110 -- i will take on the values 10,8,6,4,2 within the loop
2116 If the lower bound is greater than the upper bound (or less than,
2117 in the <literal>REVERSE</> case), the loop body is not
2118 executed at all. No error is raised.
2122 If a <replaceable>label</replaceable> is attached to the
2123 <literal>FOR</> loop then the integer loop variable can be
2124 referenced with a qualified name, using that
2125 <replaceable>label</replaceable>.
2130 <sect2 id="plpgsql-records-iterating">
2131 <title>Looping Through Query Results</title>
2134 Using a different type of <literal>FOR</> loop, you can iterate through
2135 the results of a query and manipulate that data
2136 accordingly. The syntax is:
2138 <optional> <<<replaceable>label</replaceable>>> </optional>
2139 FOR <replaceable>target</replaceable> IN <replaceable>query</replaceable> LOOP
2140 <replaceable>statements</replaceable>
2141 END LOOP <optional> <replaceable>label</replaceable> </optional>;
2143 The <replaceable>target</replaceable> is a record variable, row variable,
2144 or comma-separated list of scalar variables.
2145 The <replaceable>target</replaceable> is successively assigned each row
2146 resulting from the <replaceable>query</replaceable> and the loop body is
2147 executed for each row. Here is an example:
2149 CREATE FUNCTION cs_refresh_mviews() RETURNS integer AS $$
2153 PERFORM cs_log('Refreshing materialized views...');
2155 FOR mviews IN SELECT * FROM cs_materialized_views ORDER BY sort_key LOOP
2157 -- Now "mviews" has one record from cs_materialized_views
2159 PERFORM cs_log('Refreshing materialized view '
2160 || quote_ident(mviews.mv_name) || ' ...');
2161 EXECUTE 'TRUNCATE TABLE ' || quote_ident(mviews.mv_name);
2162 EXECUTE 'INSERT INTO '
2163 || quote_ident(mviews.mv_name) || ' '
2167 PERFORM cs_log('Done refreshing materialized views.');
2170 $$ LANGUAGE plpgsql;
2173 If the loop is terminated by an <literal>EXIT</> statement, the last
2174 assigned row value is still accessible after the loop.
2178 The <replaceable>query</replaceable> used in this type of <literal>FOR</>
2179 statement can be any SQL command that returns rows to the caller:
2180 <command>SELECT</> is the most common case,
2181 but you can also use <command>INSERT</>, <command>UPDATE</>, or
2182 <command>DELETE</> with a <literal>RETURNING</> clause. Some utility
2183 commands such as <command>EXPLAIN</> will work too.
2187 <application>PL/pgSQL</> variables are substituted into the query text,
2188 and the query plan is cached for possible re-use, as discussed in
2189 detail in <xref linkend="plpgsql-var-subst"> and
2190 <xref linkend="plpgsql-plan-caching">.
2194 The <literal>FOR-IN-EXECUTE</> statement is another way to iterate over
2197 <optional> <<<replaceable>label</replaceable>>> </optional>
2198 FOR <replaceable>target</replaceable> IN EXECUTE <replaceable>text_expression</replaceable> <optional> USING <replaceable>expression</replaceable> <optional>, ... </optional> </optional> LOOP
2199 <replaceable>statements</replaceable>
2200 END LOOP <optional> <replaceable>label</replaceable> </optional>;
2202 This is like the previous form, except that the source query
2203 is specified as a string expression, which is evaluated and replanned
2204 on each entry to the <literal>FOR</> loop. This allows the programmer to
2205 choose the speed of a preplanned query or the flexibility of a dynamic
2206 query, just as with a plain <command>EXECUTE</command> statement.
2207 As with <command>EXECUTE</command>, parameter values can be inserted
2208 into the dynamic command via <literal>USING</>.
2212 Another way to specify the query whose results should be iterated
2213 through is to declare it as a cursor. This is described in
2214 <xref linkend="plpgsql-cursor-for-loop">.
2218 <sect2 id="plpgsql-error-trapping">
2219 <title>Trapping Errors</title>
2222 <primary>exceptions</primary>
2223 <secondary>in PL/PgSQL</secondary>
2227 By default, any error occurring in a <application>PL/pgSQL</>
2228 function aborts execution of the function, and indeed of the
2229 surrounding transaction as well. You can trap errors and recover
2230 from them by using a <command>BEGIN</> block with an
2231 <literal>EXCEPTION</> clause. The syntax is an extension of the
2232 normal syntax for a <command>BEGIN</> block:
2235 <optional> <<<replaceable>label</replaceable>>> </optional>
2237 <replaceable>declarations</replaceable> </optional>
2239 <replaceable>statements</replaceable>
2241 WHEN <replaceable>condition</replaceable> <optional> OR <replaceable>condition</replaceable> ... </optional> THEN
2242 <replaceable>handler_statements</replaceable>
2243 <optional> WHEN <replaceable>condition</replaceable> <optional> OR <replaceable>condition</replaceable> ... </optional> THEN
2244 <replaceable>handler_statements</replaceable>
2251 If no error occurs, this form of block simply executes all the
2252 <replaceable>statements</replaceable>, and then control passes
2253 to the next statement after <literal>END</>. But if an error
2254 occurs within the <replaceable>statements</replaceable>, further
2255 processing of the <replaceable>statements</replaceable> is
2256 abandoned, and control passes to the <literal>EXCEPTION</> list.
2257 The list is searched for the first <replaceable>condition</replaceable>
2258 matching the error that occurred. If a match is found, the
2259 corresponding <replaceable>handler_statements</replaceable> are
2260 executed, and then control passes to the next statement after
2261 <literal>END</>. If no match is found, the error propagates out
2262 as though the <literal>EXCEPTION</> clause were not there at all:
2263 the error can be caught by an enclosing block with
2264 <literal>EXCEPTION</>, or if there is none it aborts processing
2269 The <replaceable>condition</replaceable> names can be any of
2270 those shown in <xref linkend="errcodes-appendix">. A category
2271 name matches any error within its category. The special
2272 condition name <literal>OTHERS</> matches every error type except
2273 <literal>QUERY_CANCELED</>. (It is possible, but often unwise,
2274 to trap <literal>QUERY_CANCELED</> by name.) Condition names are
2275 not case-sensitive. Also, an error condition can be specified
2276 by <literal>SQLSTATE</> code; for example these are equivalent:
2278 WHEN division_by_zero THEN ...
2279 WHEN SQLSTATE '22012' THEN ...
2284 If a new error occurs within the selected
2285 <replaceable>handler_statements</replaceable>, it cannot be caught
2286 by this <literal>EXCEPTION</> clause, but is propagated out.
2287 A surrounding <literal>EXCEPTION</> clause could catch it.
2291 When an error is caught by an <literal>EXCEPTION</> clause,
2292 the local variables of the <application>PL/pgSQL</> function
2293 remain as they were when the error occurred, but all changes
2294 to persistent database state within the block are rolled back.
2295 As an example, consider this fragment:
2298 INSERT INTO mytab(firstname, lastname) VALUES('Tom', 'Jones');
2300 UPDATE mytab SET firstname = 'Joe' WHERE lastname = 'Jones';
2304 WHEN division_by_zero THEN
2305 RAISE NOTICE 'caught division_by_zero';
2310 When control reaches the assignment to <literal>y</>, it will
2311 fail with a <literal>division_by_zero</> error. This will be caught by
2312 the <literal>EXCEPTION</> clause. The value returned in the
2313 <command>RETURN</> statement will be the incremented value of
2314 <literal>x</>, but the effects of the <command>UPDATE</> command will
2315 have been rolled back. The <command>INSERT</> command preceding the
2316 block is not rolled back, however, so the end result is that the database
2317 contains <literal>Tom Jones</> not <literal>Joe Jones</>.
2322 A block containing an <literal>EXCEPTION</> clause is significantly
2323 more expensive to enter and exit than a block without one. Therefore,
2324 don't use <literal>EXCEPTION</> without need.
2329 Within an exception handler, the <varname>SQLSTATE</varname>
2330 variable contains the error code that corresponds to the
2331 exception that was raised (refer to <xref
2332 linkend="errcodes-table"> for a list of possible error
2333 codes). The <varname>SQLERRM</varname> variable contains the
2334 error message associated with the exception. These variables are
2335 undefined outside exception handlers.
2338 <example id="plpgsql-upsert-example">
2339 <title>Exceptions with <command>UPDATE</>/<command>INSERT</></title>
2342 This example uses exception handling to perform either
2343 <command>UPDATE</> or <command>INSERT</>, as appropriate:
2346 CREATE TABLE db (a INT PRIMARY KEY, b TEXT);
2348 CREATE FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS
2352 -- first try to update the key
2353 UPDATE db SET b = data WHERE a = key;
2357 -- not there, so try to insert the key
2358 -- if someone else inserts the same key concurrently,
2359 -- we could get a unique-key failure
2361 INSERT INTO db(a,b) VALUES (key, data);
2363 EXCEPTION WHEN unique_violation THEN
2364 -- do nothing, and loop to try the UPDATE again
2371 SELECT merge_db(1, 'david');
2372 SELECT merge_db(1, 'dennis');
2380 <sect1 id="plpgsql-cursors">
2381 <title>Cursors</title>
2383 <indexterm zone="plpgsql-cursors">
2384 <primary>cursor</primary>
2385 <secondary>in PL/pgSQL</secondary>
2389 Rather than executing a whole query at once, it is possible to set
2390 up a <firstterm>cursor</> that encapsulates the query, and then read
2391 the query result a few rows at a time. One reason for doing this is
2392 to avoid memory overrun when the result contains a large number of
2393 rows. (However, <application>PL/pgSQL</> users do not normally need
2394 to worry about that, since <literal>FOR</> loops automatically use a cursor
2395 internally to avoid memory problems.) A more interesting usage is to
2396 return a reference to a cursor that a function has created, allowing the
2397 caller to read the rows. This provides an efficient way to return
2398 large row sets from functions.
2401 <sect2 id="plpgsql-cursor-declarations">
2402 <title>Declaring Cursor Variables</title>
2405 All access to cursors in <application>PL/pgSQL</> goes through
2406 cursor variables, which are always of the special data type
2407 <type>refcursor</>. One way to create a cursor variable
2408 is just to declare it as a variable of type <type>refcursor</>.
2409 Another way is to use the cursor declaration syntax,
2410 which in general is:
2412 <replaceable>name</replaceable> <optional> <optional> NO </optional> SCROLL </optional> CURSOR <optional> ( <replaceable>arguments</replaceable> ) </optional> FOR <replaceable>query</replaceable>;
2414 (<literal>FOR</> can be replaced by <literal>IS</> for
2415 <productname>Oracle</productname> compatibility.)
2416 If <literal>SCROLL</> is specified, the cursor will be capable of
2417 scrolling backward; if <literal>NO SCROLL</> is specified, backward
2418 fetches will be rejected; if neither specification appears, it is
2419 query-dependent whether backward fetches will be allowed.
2420 <replaceable>arguments</replaceable>, if specified, is a
2421 comma-separated list of pairs <literal><replaceable>name</replaceable>
2422 <replaceable>datatype</replaceable></literal> that define names to be
2423 replaced by parameter values in the given query. The actual
2424 values to substitute for these names will be specified later,
2425 when the cursor is opened.
2432 curs2 CURSOR FOR SELECT * FROM tenk1;
2433 curs3 CURSOR (key integer) IS SELECT * FROM tenk1 WHERE unique1 = key;
2435 All three of these variables have the data type <type>refcursor</>,
2436 but the first can be used with any query, while the second has
2437 a fully specified query already <firstterm>bound</> to it, and the last
2438 has a parameterized query bound to it. (<literal>key</> will be
2439 replaced by an integer parameter value when the cursor is opened.)
2440 The variable <literal>curs1</>
2441 is said to be <firstterm>unbound</> since it is not bound to
2442 any particular query.
2446 <sect2 id="plpgsql-cursor-opening">
2447 <title>Opening Cursors</title>
2450 Before a cursor can be used to retrieve rows, it must be
2451 <firstterm>opened</>. (This is the equivalent action to the SQL
2452 command <command>DECLARE CURSOR</>.) <application>PL/pgSQL</> has
2453 three forms of the <command>OPEN</> statement, two of which use unbound
2454 cursor variables while the third uses a bound cursor variable.
2459 Bound cursor variables can also be used without explicitly opening the cursor,
2460 via the <command>FOR</> statement described in
2461 <xref linkend="plpgsql-cursor-for-loop">.
2466 <title><command>OPEN FOR</command> <replaceable>query</replaceable></title>
2469 OPEN <replaceable>unbound_cursorvar</replaceable> <optional> <optional> NO </optional> SCROLL </optional> FOR <replaceable>query</replaceable>;
2473 The cursor variable is opened and given the specified query to
2474 execute. The cursor cannot be open already, and it must have been
2475 declared as an unbound cursor variable (that is, as a simple
2476 <type>refcursor</> variable). The query must be a
2477 <command>SELECT</command>, or something else that returns rows
2478 (such as <command>EXPLAIN</>). The query
2479 is treated in the same way as other SQL commands in
2480 <application>PL/pgSQL</>: <application>PL/pgSQL</>
2481 variable names are substituted, and the query plan is cached for
2482 possible reuse. When a <application>PL/pgSQL</>
2483 variable is substituted into the cursor query, the value that is
2484 substituted is the one it has at the time of the <command>OPEN</>;
2485 subsequent changes to the variable will not affect the cursor's
2487 The <literal>SCROLL</> and <literal>NO SCROLL</>
2488 options have the same meanings as for a bound cursor.
2494 OPEN curs1 FOR SELECT * FROM foo WHERE key = mykey;
2500 <title><command>OPEN FOR EXECUTE</command></title>
2503 OPEN <replaceable>unbound_cursorvar</replaceable> <optional> <optional> NO </optional> SCROLL </optional> FOR EXECUTE <replaceable class="command">query_string</replaceable>
2504 <optional> USING <replaceable>expression</replaceable> <optional>, ... </optional> </optional>;
2508 The cursor variable is opened and given the specified query to
2509 execute. The cursor cannot be open already, and it must have been
2510 declared as an unbound cursor variable (that is, as a simple
2511 <type>refcursor</> variable). The query is specified as a string
2512 expression, in the same way as in the <command>EXECUTE</command>
2513 command. As usual, this gives flexibility so the query plan can vary
2514 from one run to the next (see <xref linkend="plpgsql-plan-caching">),
2515 and it also means that variable substitution is not done on the
2516 command string. As with <command>EXECUTE</command>, parameter values
2517 can be inserted into the dynamic command via <literal>USING</>.
2518 The <literal>SCROLL</> and
2519 <literal>NO SCROLL</> options have the same meanings as for a bound
2526 OPEN curs1 FOR EXECUTE 'SELECT * FROM ' || quote_ident(tabname)
2527 || ' WHERE col1 = $1' USING keyvalue;
2529 In this example, the table name is inserted into the query textually,
2530 so use of <function>quote_ident()</> is recommended to guard against
2531 SQL injection. The comparison value for <literal>col1</> is inserted
2532 via a <literal>USING</> parameter, so it needs no quoting.
2537 <title>Opening a Bound Cursor</title>
2540 OPEN <replaceable>bound_cursorvar</replaceable> <optional> ( <replaceable>argument_values</replaceable> ) </optional>;
2544 This form of <command>OPEN</command> is used to open a cursor
2545 variable whose query was bound to it when it was declared. The
2546 cursor cannot be open already. A list of actual argument value
2547 expressions must appear if and only if the cursor was declared to
2548 take arguments. These values will be substituted in the query.
2549 The query plan for a bound cursor is always considered cacheable;
2550 there is no equivalent of <command>EXECUTE</command> in this case.
2551 Notice that <literal>SCROLL</> and
2552 <literal>NO SCROLL</> cannot be specified, as the cursor's scrolling
2553 behavior was already determined.
2557 Note that because variable substitution is done on the bound
2558 cursor's query, there are two ways to pass values into the cursor:
2559 either with an explicit argument to <command>OPEN</>, or
2560 implicitly by referencing a <application>PL/pgSQL</> variable
2561 in the query. However, only variables declared before the bound
2562 cursor was declared will be substituted into it. In either case
2563 the value to be passed is determined at the time of the
2577 <sect2 id="plpgsql-cursor-using">
2578 <title>Using Cursors</title>
2581 Once a cursor has been opened, it can be manipulated with the
2582 statements described here.
2586 These manipulations need not occur in the same function that
2587 opened the cursor to begin with. You can return a <type>refcursor</>
2588 value out of a function and let the caller operate on the cursor.
2589 (Internally, a <type>refcursor</> value is simply the string name
2590 of a so-called portal containing the active query for the cursor. This name
2591 can be passed around, assigned to other <type>refcursor</> variables,
2592 and so on, without disturbing the portal.)
2596 All portals are implicitly closed at transaction end. Therefore
2597 a <type>refcursor</> value is usable to reference an open cursor
2598 only until the end of the transaction.
2602 <title><literal>FETCH</></title>
2605 FETCH <optional> <replaceable>direction</replaceable> { FROM | IN } </optional> <replaceable>cursor</replaceable> INTO <replaceable>target</replaceable>;
2609 <command>FETCH</command> retrieves the next row from the
2610 cursor into a target, which might be a row variable, a record
2611 variable, or a comma-separated list of simple variables, just like
2612 <command>SELECT INTO</command>. If there is no next row, the
2613 target is set to NULL(s). As with <command>SELECT
2614 INTO</command>, the special variable <literal>FOUND</literal> can
2615 be checked to see whether a row was obtained or not.
2619 The <replaceable>direction</replaceable> clause can be any of the
2620 variants allowed in the SQL <xref linkend="sql-fetch">
2621 command except the ones that can fetch
2622 more than one row; namely, it can be
2627 <literal>ABSOLUTE</> <replaceable>count</replaceable>,
2628 <literal>RELATIVE</> <replaceable>count</replaceable>,
2629 <literal>FORWARD</>, or
2630 <literal>BACKWARD</>.
2631 Omitting <replaceable>direction</replaceable> is the same
2632 as specifying <literal>NEXT</>.
2633 <replaceable>direction</replaceable> values that require moving
2634 backward are likely to fail unless the cursor was declared or opened
2635 with the <literal>SCROLL</> option.
2639 <replaceable>cursor</replaceable> must be the name of a <type>refcursor</>
2640 variable that references an open cursor portal.
2646 FETCH curs1 INTO rowvar;
2647 FETCH curs2 INTO foo, bar, baz;
2648 FETCH LAST FROM curs3 INTO x, y;
2649 FETCH RELATIVE -2 FROM curs4 INTO x;
2655 <title><literal>MOVE</></title>
2658 MOVE <optional> <replaceable>direction</replaceable> { FROM | IN } </optional> <replaceable>cursor</replaceable>;
2662 <command>MOVE</command> repositions a cursor without retrieving
2663 any data. <command>MOVE</command> works exactly like the
2664 <command>FETCH</command> command, except it only repositions the
2665 cursor and does not return the row moved to. As with <command>SELECT
2666 INTO</command>, the special variable <literal>FOUND</literal> can
2667 be checked to see whether there was a next row to move to.
2671 The <replaceable>direction</replaceable> clause can be any of the
2672 variants allowed in the SQL <xref linkend="sql-fetch">
2678 <literal>ABSOLUTE</> <replaceable>count</replaceable>,
2679 <literal>RELATIVE</> <replaceable>count</replaceable>,
2681 <literal>FORWARD</> <optional> <replaceable>count</replaceable> | <literal>ALL</> </optional>, or
2682 <literal>BACKWARD</> <optional> <replaceable>count</replaceable> | <literal>ALL</> </optional>.
2683 Omitting <replaceable>direction</replaceable> is the same
2684 as specifying <literal>NEXT</>.
2685 <replaceable>direction</replaceable> values that require moving
2686 backward are likely to fail unless the cursor was declared or opened
2687 with the <literal>SCROLL</> option.
2694 MOVE LAST FROM curs3;
2695 MOVE RELATIVE -2 FROM curs4;
2696 MOVE FORWARD 2 FROM curs4;
2702 <title><literal>UPDATE/DELETE WHERE CURRENT OF</></title>
2705 UPDATE <replaceable>table</replaceable> SET ... WHERE CURRENT OF <replaceable>cursor</replaceable>;
2706 DELETE FROM <replaceable>table</replaceable> WHERE CURRENT OF <replaceable>cursor</replaceable>;
2710 When a cursor is positioned on a table row, that row can be updated
2711 or deleted using the cursor to identify the row. There are
2712 restrictions on what the cursor's query can be (in particular,
2713 no grouping) and it's best to use <literal>FOR UPDATE</> in the
2714 cursor. For more information see the
2715 <xref linkend="sql-declare">
2722 UPDATE foo SET dataval = myval WHERE CURRENT OF curs1;
2728 <title><literal>CLOSE</></title>
2731 CLOSE <replaceable>cursor</replaceable>;
2735 <command>CLOSE</command> closes the portal underlying an open
2736 cursor. This can be used to release resources earlier than end of
2737 transaction, or to free up the cursor variable to be opened again.
2749 <title>Returning Cursors</title>
2752 <application>PL/pgSQL</> functions can return cursors to the
2753 caller. This is useful to return multiple rows or columns,
2754 especially with very large result sets. To do this, the function
2755 opens the cursor and returns the cursor name to the caller (or simply
2756 opens the cursor using a portal name specified by or otherwise known
2757 to the caller). The caller can then fetch rows from the cursor. The
2758 cursor can be closed by the caller, or it will be closed automatically
2759 when the transaction closes.
2763 The portal name used for a cursor can be specified by the
2764 programmer or automatically generated. To specify a portal name,
2765 simply assign a string to the <type>refcursor</> variable before
2766 opening it. The string value of the <type>refcursor</> variable
2767 will be used by <command>OPEN</> as the name of the underlying portal.
2768 However, if the <type>refcursor</> variable is null,
2769 <command>OPEN</> automatically generates a name that does not
2770 conflict with any existing portal, and assigns it to the
2771 <type>refcursor</> variable.
2776 A bound cursor variable is initialized to the string value
2777 representing its name, so that the portal name is the same as
2778 the cursor variable name, unless the programmer overrides it
2779 by assignment before opening the cursor. But an unbound cursor
2780 variable defaults to the null value initially, so it will receive
2781 an automatically-generated unique name, unless overridden.
2786 The following example shows one way a cursor name can be supplied by
2790 CREATE TABLE test (col text);
2791 INSERT INTO test VALUES ('123');
2793 CREATE FUNCTION reffunc(refcursor) RETURNS refcursor AS '
2795 OPEN $1 FOR SELECT col FROM test;
2801 SELECT reffunc('funccursor');
2802 FETCH ALL IN funccursor;
2808 The following example uses automatic cursor name generation:
2811 CREATE FUNCTION reffunc2() RETURNS refcursor AS '
2815 OPEN ref FOR SELECT col FROM test;
2820 -- need to be in a transaction to use cursors.
2825 --------------------
2826 <unnamed cursor 1>
2829 FETCH ALL IN "<unnamed cursor 1>";
2835 The following example shows one way to return multiple cursors
2836 from a single function:
2839 CREATE FUNCTION myfunc(refcursor, refcursor) RETURNS SETOF refcursor AS $$
2841 OPEN $1 FOR SELECT * FROM table_1;
2843 OPEN $2 FOR SELECT * FROM table_2;
2846 $$ LANGUAGE plpgsql;
2848 -- need to be in a transaction to use cursors.
2851 SELECT * FROM myfunc('a', 'b');
2861 <sect2 id="plpgsql-cursor-for-loop">
2862 <title>Looping Through a Cursor's Result</title>
2865 There is a variant of the <command>FOR</> statement that allows
2866 iterating through the rows returned by a cursor. The syntax is:
2869 <optional> <<<replaceable>label</replaceable>>> </optional>
2870 FOR <replaceable>recordvar</replaceable> IN <replaceable>bound_cursorvar</replaceable> <optional> ( <replaceable>argument_values</replaceable> ) </optional> LOOP
2871 <replaceable>statements</replaceable>
2872 END LOOP <optional> <replaceable>label</replaceable> </optional>;
2875 The cursor variable must have been bound to some query when it was
2876 declared, and it <emphasis>cannot</> be open already. The
2877 <command>FOR</> statement automatically opens the cursor, and it closes
2878 the cursor again when the loop exits. A list of actual argument value
2879 expressions must appear if and only if the cursor was declared to take
2880 arguments. These values will be substituted in the query, in just
2881 the same way as during an <command>OPEN</>.
2882 The variable <replaceable>recordvar</replaceable> is automatically
2883 defined as type <type>record</> and exists only inside the loop (any
2884 existing definition of the variable name is ignored within the loop).
2885 Each row returned by the cursor is successively assigned to this
2886 record variable and the loop body is executed.
2892 <sect1 id="plpgsql-errors-and-messages">
2893 <title>Errors and Messages</title>
2896 <primary>RAISE</primary>
2900 <primary>reporting errors</primary>
2901 <secondary>in PL/PgSQL</secondary>
2905 Use the <command>RAISE</command> statement to report messages and
2909 RAISE <optional> <replaceable class="parameter">level</replaceable> </optional> '<replaceable class="parameter">format</replaceable>' <optional>, <replaceable class="parameter">expression</replaceable> <optional>, ... </optional></optional> <optional> USING <replaceable class="parameter">option</replaceable> = <replaceable class="parameter">expression</replaceable> <optional>, ... </optional> </optional>;
2910 RAISE <optional> <replaceable class="parameter">level</replaceable> </optional> <replaceable class="parameter">condition_name</> <optional> USING <replaceable class="parameter">option</replaceable> = <replaceable class="parameter">expression</replaceable> <optional>, ... </optional> </optional>;
2911 RAISE <optional> <replaceable class="parameter">level</replaceable> </optional> SQLSTATE '<replaceable class="parameter">sqlstate</>' <optional> USING <replaceable class="parameter">option</replaceable> = <replaceable class="parameter">expression</replaceable> <optional>, ... </optional> </optional>;
2912 RAISE <optional> <replaceable class="parameter">level</replaceable> </optional> USING <replaceable class="parameter">option</replaceable> = <replaceable class="parameter">expression</replaceable> <optional>, ... </optional>;
2916 The <replaceable class="parameter">level</replaceable> option specifies
2917 the error severity. Allowed levels are <literal>DEBUG</literal>,
2918 <literal>LOG</literal>, <literal>INFO</literal>,
2919 <literal>NOTICE</literal>, <literal>WARNING</literal>,
2920 and <literal>EXCEPTION</literal>, with <literal>EXCEPTION</literal>
2922 <literal>EXCEPTION</literal> raises an error (which normally aborts the
2923 current transaction); the other levels only generate messages of different
2925 Whether messages of a particular priority are reported to the client,
2926 written to the server log, or both is controlled by the
2927 <xref linkend="guc-log-min-messages"> and
2928 <xref linkend="guc-client-min-messages"> configuration
2929 variables. See <xref linkend="runtime-config"> for more
2934 After <replaceable class="parameter">level</replaceable> if any,
2935 you can write a <replaceable class="parameter">format</replaceable>
2936 (which must be a simple string literal, not an expression). The
2937 format string specifies the error message text to be reported.
2938 The format string can be followed
2939 by optional argument expressions to be inserted into the message.
2940 Inside the format string, <literal>%</literal> is replaced by the
2941 string representation of the next optional argument's value. Write
2942 <literal>%%</literal> to emit a literal <literal>%</literal>.
2946 In this example, the value of <literal>v_job_id</> will replace the
2947 <literal>%</literal> in the string:
2949 RAISE NOTICE 'Calling cs_create_job(%)', v_job_id;
2954 You can attach additional information to the error report by writing
2955 <literal>USING</> followed by <replaceable
2956 class="parameter">option</replaceable> = <replaceable
2957 class="parameter">expression</replaceable> items. The allowed
2958 <replaceable class="parameter">option</replaceable> keywords are
2959 <literal>MESSAGE</>, <literal>DETAIL</>, <literal>HINT</>, and
2960 <literal>ERRCODE</>, while each <replaceable
2961 class="parameter">expression</replaceable> can be any string-valued
2963 <literal>MESSAGE</> sets the error message text (this option can't
2964 be used in the form of <command>RAISE</> that includes a format
2965 string before <literal>USING</>).
2966 <literal>DETAIL</> supplies an error detail message, while
2967 <literal>HINT</> supplies a hint message.
2968 <literal>ERRCODE</> specifies the error code (SQLSTATE) to report,
2969 either by condition name as shown in <xref linkend="errcodes-appendix">,
2970 or directly as a five-character SQLSTATE code.
2974 This example will abort the transaction with the given error message
2977 RAISE EXCEPTION 'Nonexistent ID --> %', user_id
2978 USING HINT = 'Please check your user id';
2983 These two examples show equivalent ways of setting the SQLSTATE:
2985 RAISE 'Duplicate user ID: %', user_id USING ERRCODE = 'unique_violation';
2986 RAISE 'Duplicate user ID: %', user_id USING ERRCODE = '23505';
2991 There is a second <command>RAISE</> syntax in which the main argument
2992 is the condition name or SQLSTATE to be reported, for example:
2994 RAISE division_by_zero;
2995 RAISE SQLSTATE '22012';
2997 In this syntax, <literal>USING</> can be used to supply a custom
2998 error message, detail, or hint. Another way to do the earlier
3001 RAISE unique_violation USING MESSAGE = 'Duplicate user ID: ' || user_id;
3006 Still another variant is to write <literal>RAISE USING</> or <literal>RAISE
3007 <replaceable class="parameter">level</replaceable> USING</> and put
3008 everything else into the <literal>USING</> list.
3012 The last variant of <command>RAISE</> has no parameters at all.
3013 This form can only be used inside a <literal>BEGIN</> block's
3014 <literal>EXCEPTION</> clause;
3015 it causes the error currently being handled to be re-thrown.
3020 Before <productname>PostgreSQL</> 9.1, <command>RAISE</> without
3021 parameters was interpreted as re-throwing the error from the block
3022 containing the active exception handler. Thus an <literal>EXCEPTION</>
3023 clause nested within that handler could not catch it, even if the
3024 <command>RAISE</> was within the nested <literal>EXCEPTION</> clause's
3025 block. This was deemed surprising as well as being incompatible with
3031 If no condition name nor SQLSTATE is specified in a
3032 <command>RAISE EXCEPTION</command> command, the default is to use
3033 <literal>RAISE_EXCEPTION</> (<literal>P0001</>). If no message
3034 text is specified, the default is to use the condition name or
3035 SQLSTATE as message text.
3040 When specifying an error code by SQLSTATE code, you are not
3041 limited to the predefined error codes, but can select any
3042 error code consisting of five digits and/or upper-case ASCII
3043 letters, other than <literal>00000</>. It is recommended that
3044 you avoid throwing error codes that end in three zeroes, because
3045 these are category codes and can only be trapped by trapping
3052 <sect1 id="plpgsql-trigger">
3053 <title>Trigger Procedures</title>
3055 <indexterm zone="plpgsql-trigger">
3056 <primary>trigger</primary>
3057 <secondary>in PL/pgSQL</secondary>
3061 <application>PL/pgSQL</application> can be used to define trigger
3062 procedures. A trigger procedure is created with the
3063 <command>CREATE FUNCTION</> command, declaring it as a function with
3064 no arguments and a return type of <type>trigger</type>. Note that
3065 the function must be declared with no arguments even if it expects
3066 to receive arguments specified in <command>CREATE TRIGGER</> —
3067 trigger arguments are passed via <varname>TG_ARGV</>, as described
3072 When a <application>PL/pgSQL</application> function is called as a
3073 trigger, several special variables are created automatically in the
3074 top-level block. They are:
3078 <term><varname>NEW</varname></term>
3081 Data type <type>RECORD</type>; variable holding the new
3082 database row for <command>INSERT</>/<command>UPDATE</> operations in row-level
3083 triggers. This variable is <symbol>NULL</symbol> in statement-level triggers
3084 and for <command>DELETE</command> operations.
3090 <term><varname>OLD</varname></term>
3093 Data type <type>RECORD</type>; variable holding the old
3094 database row for <command>UPDATE</>/<command>DELETE</> operations in row-level
3095 triggers. This variable is <symbol>NULL</symbol> in statement-level triggers
3096 and for <command>INSERT</command> operations.
3102 <term><varname>TG_NAME</varname></term>
3105 Data type <type>name</type>; variable that contains the name of the trigger actually
3112 <term><varname>TG_WHEN</varname></term>
3115 Data type <type>text</type>; a string of either
3116 <literal>BEFORE</literal> or <literal>AFTER</literal>
3117 depending on the trigger's definition.
3123 <term><varname>TG_LEVEL</varname></term>
3126 Data type <type>text</type>; a string of either
3127 <literal>ROW</literal> or <literal>STATEMENT</literal>
3128 depending on the trigger's definition.
3134 <term><varname>TG_OP</varname></term>
3137 Data type <type>text</type>; a string of
3138 <literal>INSERT</literal>, <literal>UPDATE</literal>,
3139 <literal>DELETE</literal>, or <literal>TRUNCATE</>
3140 telling for which operation the trigger was fired.
3146 <term><varname>TG_RELID</varname></term>
3149 Data type <type>oid</type>; the object ID of the table that caused the
3156 <term><varname>TG_RELNAME</varname></term>
3159 Data type <type>name</type>; the name of the table that caused the trigger
3160 invocation. This is now deprecated, and could disappear in a future
3161 release. Use <literal>TG_TABLE_NAME</> instead.
3167 <term><varname>TG_TABLE_NAME</varname></term>
3170 Data type <type>name</type>; the name of the table that
3171 caused the trigger invocation.
3177 <term><varname>TG_TABLE_SCHEMA</varname></term>
3180 Data type <type>name</type>; the name of the schema of the
3181 table that caused the trigger invocation.
3187 <term><varname>TG_NARGS</varname></term>
3190 Data type <type>integer</type>; the number of arguments given to the trigger
3191 procedure in the <command>CREATE TRIGGER</command> statement.
3197 <term><varname>TG_ARGV[]</varname></term>
3200 Data type array of <type>text</type>; the arguments from
3201 the <command>CREATE TRIGGER</command> statement.
3202 The index counts from 0. Invalid
3203 indexes (less than 0 or greater than or equal to <varname>tg_nargs</>)
3204 result in a null value.
3212 A trigger function must return either <symbol>NULL</symbol> or a
3213 record/row value having exactly the structure of the table the
3214 trigger was fired for.
3218 Row-level triggers fired <literal>BEFORE</> can return null to signal the
3219 trigger manager to skip the rest of the operation for this row
3220 (i.e., subsequent triggers are not fired, and the
3221 <command>INSERT</>/<command>UPDATE</>/<command>DELETE</> does not occur
3222 for this row). If a nonnull
3223 value is returned then the operation proceeds with that row value.
3224 Returning a row value different from the original value
3225 of <varname>NEW</> alters the row that will be inserted or
3226 updated. Thus, if the trigger function wants the triggering
3227 action to succeed normally without altering the row
3228 value, <varname>NEW</varname> (or a value equal thereto) has to be
3229 returned. To alter the row to be stored, it is possible to
3230 replace single values directly in <varname>NEW</> and return the
3231 modified <varname>NEW</>, or to build a complete new record/row to
3232 return. In the case of a before-trigger
3233 on <command>DELETE</command>, the returned value has no direct
3234 effect, but it has to be nonnull to allow the trigger action to
3235 proceed. Note that <varname>NEW</varname> is null
3236 in <command>DELETE</command> triggers, so returning that is
3237 usually not sensible. A useful idiom in <command>DELETE</command>
3238 triggers might be to return <varname>OLD</varname>.
3242 The return value of a row-level trigger
3243 fired <literal>AFTER</literal> or a statement-level trigger
3244 fired <literal>BEFORE</> or <literal>AFTER</> is
3245 always ignored; it might as well be null. However, any of these types of
3246 triggers might still abort the entire operation by raising an error.
3250 <xref linkend="plpgsql-trigger-example"> shows an example of a
3251 trigger procedure in <application>PL/pgSQL</application>.
3254 <example id="plpgsql-trigger-example">
3255 <title>A <application>PL/pgSQL</application> Trigger Procedure</title>
3258 This example trigger ensures that any time a row is inserted or updated
3259 in the table, the current user name and time are stamped into the
3260 row. And it checks that an employee's name is given and that the
3261 salary is a positive value.
3268 last_date timestamp,
3272 CREATE FUNCTION emp_stamp() RETURNS trigger AS $emp_stamp$
3274 -- Check that empname and salary are given
3275 IF NEW.empname IS NULL THEN
3276 RAISE EXCEPTION 'empname cannot be null';
3278 IF NEW.salary IS NULL THEN
3279 RAISE EXCEPTION '% cannot have null salary', NEW.empname;
3282 -- Who works for us when she must pay for it?
3283 IF NEW.salary < 0 THEN
3284 RAISE EXCEPTION '% cannot have a negative salary', NEW.empname;
3287 -- Remember who changed the payroll when
3288 NEW.last_date := current_timestamp;
3289 NEW.last_user := current_user;
3292 $emp_stamp$ LANGUAGE plpgsql;
3294 CREATE TRIGGER emp_stamp BEFORE INSERT OR UPDATE ON emp
3295 FOR EACH ROW EXECUTE PROCEDURE emp_stamp();
3300 Another way to log changes to a table involves creating a new table that
3301 holds a row for each insert, update, or delete that occurs. This approach
3302 can be thought of as auditing changes to a table.
3303 <xref linkend="plpgsql-trigger-audit-example"> shows an example of an
3304 audit trigger procedure in <application>PL/pgSQL</application>.
3307 <example id="plpgsql-trigger-audit-example">
3308 <title>A <application>PL/pgSQL</application> Trigger Procedure For Auditing</title>
3311 This example trigger ensures that any insert, update or delete of a row
3312 in the <literal>emp</literal> table is recorded (i.e., audited) in the <literal>emp_audit</literal> table.
3313 The current time and user name are stamped into the row, together with
3314 the type of operation performed on it.
3319 empname text NOT NULL,
3323 CREATE TABLE emp_audit(
3324 operation char(1) NOT NULL,
3325 stamp timestamp NOT NULL,
3326 userid text NOT NULL,
3327 empname text NOT NULL,
3331 CREATE OR REPLACE FUNCTION process_emp_audit() RETURNS TRIGGER AS $emp_audit$
3334 -- Create a row in emp_audit to reflect the operation performed on emp,
3335 -- make use of the special variable TG_OP to work out the operation.
3337 IF (TG_OP = 'DELETE') THEN
3338 INSERT INTO emp_audit SELECT 'D', now(), user, OLD.*;
3340 ELSIF (TG_OP = 'UPDATE') THEN
3341 INSERT INTO emp_audit SELECT 'U', now(), user, NEW.*;
3343 ELSIF (TG_OP = 'INSERT') THEN
3344 INSERT INTO emp_audit SELECT 'I', now(), user, NEW.*;
3347 RETURN NULL; -- result is ignored since this is an AFTER trigger
3349 $emp_audit$ LANGUAGE plpgsql;
3351 CREATE TRIGGER emp_audit
3352 AFTER INSERT OR UPDATE OR DELETE ON emp
3353 FOR EACH ROW EXECUTE PROCEDURE process_emp_audit();
3358 One use of triggers is to maintain a summary table
3359 of another table. The resulting summary can be used in place of the
3360 original table for certain queries — often with vastly reduced run
3362 This technique is commonly used in Data Warehousing, where the tables
3363 of measured or observed data (called fact tables) might be extremely large.
3364 <xref linkend="plpgsql-trigger-summary-example"> shows an example of a
3365 trigger procedure in <application>PL/pgSQL</application> that maintains
3366 a summary table for a fact table in a data warehouse.
3370 <example id="plpgsql-trigger-summary-example">
3371 <title>A <application>PL/pgSQL</application> Trigger Procedure For Maintaining A Summary Table</title>
3374 The schema detailed here is partly based on the <emphasis>Grocery Store
3375 </emphasis> example from <emphasis>The Data Warehouse Toolkit</emphasis>
3381 -- Main tables - time dimension and sales fact.
3383 CREATE TABLE time_dimension (
3384 time_key integer NOT NULL,
3385 day_of_week integer NOT NULL,
3386 day_of_month integer NOT NULL,
3387 month integer NOT NULL,
3388 quarter integer NOT NULL,
3389 year integer NOT NULL
3391 CREATE UNIQUE INDEX time_dimension_key ON time_dimension(time_key);
3393 CREATE TABLE sales_fact (
3394 time_key integer NOT NULL,
3395 product_key integer NOT NULL,
3396 store_key integer NOT NULL,
3397 amount_sold numeric(12,2) NOT NULL,
3398 units_sold integer NOT NULL,
3399 amount_cost numeric(12,2) NOT NULL
3401 CREATE INDEX sales_fact_time ON sales_fact(time_key);
3404 -- Summary table - sales by time.
3406 CREATE TABLE sales_summary_bytime (
3407 time_key integer NOT NULL,
3408 amount_sold numeric(15,2) NOT NULL,
3409 units_sold numeric(12) NOT NULL,
3410 amount_cost numeric(15,2) NOT NULL
3412 CREATE UNIQUE INDEX sales_summary_bytime_key ON sales_summary_bytime(time_key);
3415 -- Function and trigger to amend summarized column(s) on UPDATE, INSERT, DELETE.
3417 CREATE OR REPLACE FUNCTION maint_sales_summary_bytime() RETURNS TRIGGER
3418 AS $maint_sales_summary_bytime$
3420 delta_time_key integer;
3421 delta_amount_sold numeric(15,2);
3422 delta_units_sold numeric(12);
3423 delta_amount_cost numeric(15,2);
3426 -- Work out the increment/decrement amount(s).
3427 IF (TG_OP = 'DELETE') THEN
3429 delta_time_key = OLD.time_key;
3430 delta_amount_sold = -1 * OLD.amount_sold;
3431 delta_units_sold = -1 * OLD.units_sold;
3432 delta_amount_cost = -1 * OLD.amount_cost;
3434 ELSIF (TG_OP = 'UPDATE') THEN
3436 -- forbid updates that change the time_key -
3437 -- (probably not too onerous, as DELETE + INSERT is how most
3438 -- changes will be made).
3439 IF ( OLD.time_key != NEW.time_key) THEN
3440 RAISE EXCEPTION 'Update of time_key : % -> % not allowed',
3441 OLD.time_key, NEW.time_key;
3444 delta_time_key = OLD.time_key;
3445 delta_amount_sold = NEW.amount_sold - OLD.amount_sold;
3446 delta_units_sold = NEW.units_sold - OLD.units_sold;
3447 delta_amount_cost = NEW.amount_cost - OLD.amount_cost;
3449 ELSIF (TG_OP = 'INSERT') THEN
3451 delta_time_key = NEW.time_key;
3452 delta_amount_sold = NEW.amount_sold;
3453 delta_units_sold = NEW.units_sold;
3454 delta_amount_cost = NEW.amount_cost;
3459 -- Insert or update the summary row with the new values.
3460 <<insert_update>>
3462 UPDATE sales_summary_bytime
3463 SET amount_sold = amount_sold + delta_amount_sold,
3464 units_sold = units_sold + delta_units_sold,
3465 amount_cost = amount_cost + delta_amount_cost
3466 WHERE time_key = delta_time_key;
3468 EXIT insert_update WHEN found;
3471 INSERT INTO sales_summary_bytime (
3486 WHEN UNIQUE_VIOLATION THEN
3489 END LOOP insert_update;
3494 $maint_sales_summary_bytime$ LANGUAGE plpgsql;
3496 CREATE TRIGGER maint_sales_summary_bytime
3497 AFTER INSERT OR UPDATE OR DELETE ON sales_fact
3498 FOR EACH ROW EXECUTE PROCEDURE maint_sales_summary_bytime();
3500 INSERT INTO sales_fact VALUES(1,1,1,10,3,15);
3501 INSERT INTO sales_fact VALUES(1,2,1,20,5,35);
3502 INSERT INTO sales_fact VALUES(2,2,1,40,15,135);
3503 INSERT INTO sales_fact VALUES(2,3,1,10,1,13);
3504 SELECT * FROM sales_summary_bytime;
3505 DELETE FROM sales_fact WHERE product_key = 1;
3506 SELECT * FROM sales_summary_bytime;
3507 UPDATE sales_fact SET units_sold = units_sold * 2;
3508 SELECT * FROM sales_summary_bytime;
3514 <sect1 id="plpgsql-implementation">
3515 <title><application>PL/pgSQL</> Under the Hood</title>
3518 This section discusses some implementation details that are
3519 frequently important for <application>PL/pgSQL</> users to know.
3522 <sect2 id="plpgsql-var-subst">
3523 <title>Variable Substitution</title>
3526 SQL statements and expressions within a <application>PL/pgSQL</> function
3527 can refer to variables and parameters of the function. Behind the scenes,
3528 <application>PL/pgSQL</> substitutes query parameters for such references.
3529 Parameters will only be substituted in places where a parameter or
3530 column reference is syntactically allowed. As an extreme case, consider
3531 this example of poor programming style:
3533 INSERT INTO foo (foo) VALUES (foo);
3535 The first occurrence of <literal>foo</> must syntactically be a table
3536 name, so it will not be substituted, even if the function has a variable
3537 named <literal>foo</>. The second occurrence must be the name of a
3538 column of the table, so it will not be substituted either. Only the
3539 third occurrence is a candidate to be a reference to the function's
3545 <productname>PostgreSQL</productname> versions before 9.0 would try
3546 to substitute the variable in all three cases, leading to syntax errors.
3551 Since the names of variables are syntactically no different from the names
3552 of table columns, there can be ambiguity in statements that also refer to
3553 tables: is a given name meant to refer to a table column, or a variable?
3554 Let's change the previous example to
3556 INSERT INTO dest (col) SELECT foo + bar FROM src;
3558 Here, <literal>dest</> and <literal>src</> must be table names, and
3559 <literal>col</> must be a column of <literal>dest</>, but <literal>foo</>
3560 and <literal>bar</> might reasonably be either variables of the function
3561 or columns of <literal>src</>.
3565 By default, <application>PL/pgSQL</> will report an error if a name
3566 in a SQL statement could refer to either a variable or a table column.
3567 You can fix such a problem by renaming the variable or column,
3568 or by qualifying the ambiguous reference, or by telling
3569 <application>PL/pgSQL</> which interpretation to prefer.
3573 The simplest solution is to rename the variable or column.
3574 A common coding rule is to use a
3575 different naming convention for <application>PL/pgSQL</application>
3576 variables than you use for column names. For example,
3577 if you consistently name function variables
3578 <literal>v_<replaceable>something</></literal> while none of your
3579 column names start with <literal>v_</>, no conflicts will occur.
3583 Alternatively you can qualify ambiguous references to make them clear.
3584 In the above example, <literal>src.foo</> would be an unambiguous reference
3585 to the table column. To create an unambiguous reference to a variable,
3586 declare it in a labeled block and use the block's label
3587 (see <xref linkend="plpgsql-structure">). For example,
3589 <<block>>
3594 INSERT INTO dest (col) SELECT block.foo + bar FROM src;
3596 Here <literal>block.foo</> means the variable even if there is a column
3597 <literal>foo</> in <literal>src</>. Function parameters, as well as
3598 special variables such as <literal>FOUND</>, can be qualified by the
3599 function's name, because they are implicitly declared in an outer block
3600 labeled with the function's name.
3604 Sometimes it is impractical to fix all the ambiguous references in a
3605 large body of <application>PL/pgSQL</> code. In such cases you can
3606 specify that <application>PL/pgSQL</> should resolve ambiguous references
3607 as the variable (which is compatible with <application>PL/pgSQL</>'s
3608 behavior before <productname>PostgreSQL</productname> 9.0), or as the
3609 table column (which is compatible with some other systems such as
3610 <productname>Oracle</productname>).
3614 <primary><varname>plpgsql.variable_conflict</> configuration parameter</primary>
3618 To change this behavior on a system-wide basis, set the configuration
3619 parameter <literal>plpgsql.variable_conflict</> to one of
3620 <literal>error</>, <literal>use_variable</>, or
3621 <literal>use_column</> (where <literal>error</> is the factory default).
3622 This parameter affects subsequent compilations
3623 of statements in <application>PL/pgSQL</> functions, but not statements
3624 already compiled in the current session. To set the parameter before
3625 <application>PL/pgSQL</> has been loaded, it is necessary to have added
3626 <quote><literal>plpgsql</></> to the <xref
3627 linkend="guc-custom-variable-classes"> list in
3628 <filename>postgresql.conf</filename>. Because changing this setting
3629 can cause unexpected changes in the behavior of <application>PL/pgSQL</>
3630 functions, it can only be changed by a superuser.
3634 You can also set the behavior on a function-by-function basis, by
3635 inserting one of these special commands at the start of the function
3638 #variable_conflict error
3639 #variable_conflict use_variable
3640 #variable_conflict use_column
3642 These commands affect only the function they are written in, and override
3643 the setting of <literal>plpgsql.variable_conflict</>. An example is
3645 CREATE FUNCTION stamp_user(id int, comment text) RETURNS void AS $$
3646 #variable_conflict use_variable
3648 curtime timestamp := now();
3650 UPDATE users SET last_modified = curtime, comment = comment
3651 WHERE users.id = id;
3653 $$ LANGUAGE plpgsql;
3655 In the <literal>UPDATE</> command, <literal>curtime</>, <literal>comment</>,
3656 and <literal>id</> will refer to the function's variable and parameters
3657 whether or not <literal>users</> has columns of those names. Notice
3658 that we had to qualify the reference to <literal>users.id</> in the
3659 <literal>WHERE</> clause to make it refer to the table column.
3660 But we did not have to qualify the reference to <literal>comment</>
3661 as a target in the <literal>UPDATE</> list, because syntactically
3662 that must be a column of <literal>users</>. We could write the same
3663 function without depending on the <literal>variable_conflict</> setting
3666 CREATE FUNCTION stamp_user(id int, comment text) RETURNS void AS $$
3669 curtime timestamp := now();
3671 UPDATE users SET last_modified = fn.curtime, comment = stamp_user.comment
3672 WHERE users.id = stamp_user.id;
3674 $$ LANGUAGE plpgsql;
3679 Variable substitution does not happen in the command string given
3680 to <command>EXECUTE</> or one of its variants. If you need to
3681 insert a varying value into such a command, do so as part of
3682 constructing the string value, or use <literal>USING</>, as illustrated in
3683 <xref linkend="plpgsql-statements-executing-dyn">.
3687 Variable substitution currently works only in <command>SELECT</>,
3688 <command>INSERT</>, <command>UPDATE</>, and <command>DELETE</> commands,
3689 because the main SQL engine allows query parameters only in these
3690 commands. To use a non-constant name or value in other statement
3691 types (generically called utility statements), you must construct
3692 the utility statement as a string and <command>EXECUTE</> it.
3697 <sect2 id="plpgsql-plan-caching">
3698 <title>Plan Caching</title>
3701 The <application>PL/pgSQL</> interpreter parses the function's source
3702 text and produces an internal binary instruction tree the first time the
3703 function is called (within each session). The instruction tree
3704 fully translates the
3705 <application>PL/pgSQL</> statement structure, but individual
3706 <acronym>SQL</acronym> expressions and <acronym>SQL</acronym> commands
3707 used in the function are not translated immediately.
3711 As each expression and <acronym>SQL</acronym> command is first
3712 executed in the function, the <application>PL/pgSQL</> interpreter
3713 creates a prepared execution plan (using the
3714 <acronym>SPI</acronym> manager's <function>SPI_prepare</function>
3715 and <function>SPI_saveplan</function>
3716 functions).<indexterm><primary>preparing a query</><secondary>in
3717 PL/pgSQL</></> Subsequent visits to that expression or command
3718 reuse the prepared plan. Thus, a function with conditional code
3719 that contains many statements for which execution plans might be
3720 required will only prepare and save those plans that are really
3721 used during the lifetime of the database connection. This can
3722 substantially reduce the total amount of time required to parse
3723 and generate execution plans for the statements in a
3724 <application>PL/pgSQL</> function. A disadvantage is that errors
3725 in a specific expression or command cannot be detected until that
3726 part of the function is reached in execution. (Trivial syntax
3727 errors will be detected during the initial parsing pass, but
3728 anything deeper will not be detected until execution.)
3732 A saved plan will be re-planned automatically if there is any schema
3733 change to any table used in the query, or if any user-defined function
3734 used in the query is redefined. This makes the re-use of prepared plans
3735 transparent in most cases, but there are corner cases where a stale plan
3736 might be re-used. An example is that dropping and re-creating a
3737 user-defined operator won't affect already-cached plans; they'll continue
3738 to call the original operator's underlying function, if that has not been
3739 changed. When necessary, the cache can be flushed by starting a fresh
3744 Because <application>PL/pgSQL</application> saves execution plans
3745 in this way, SQL commands that appear directly in a
3746 <application>PL/pgSQL</application> function must refer to the
3747 same tables and columns on every execution; that is, you cannot use
3748 a parameter as the name of a table or column in an SQL command. To get
3749 around this restriction, you can construct dynamic commands using
3750 the <application>PL/pgSQL</application> <command>EXECUTE</command>
3751 statement — at the price of constructing a new execution plan on
3756 Another important point is that the prepared plans are parameterized
3757 to allow the values of <application>PL/pgSQL</application> variables
3758 to change from one use to the next, as discussed in detail above.
3759 Sometimes this means that a plan is less efficient than it would be
3760 if generated for a specific variable value. As an example, consider
3762 SELECT * INTO myrec FROM dictionary WHERE word LIKE search_term;
3764 where <literal>search_term</> is a <application>PL/pgSQL</application>
3765 variable. The cached plan for this query will never use an index on
3766 <structfield>word</>, since the planner cannot assume that the
3767 <literal>LIKE</> pattern will be left-anchored at run time. To use
3768 an index the query must be planned with a specific constant
3769 <literal>LIKE</> pattern provided. This is another situation where
3770 <command>EXECUTE</command> can be used to force a new plan to be
3771 generated for each execution.
3775 The mutable nature of record variables presents another problem in this
3776 connection. When fields of a record variable are used in
3777 expressions or statements, the data types of the fields must not
3778 change from one call of the function to the next, since each
3779 expression will be planned using the data type that is present
3780 when the expression is first reached. <command>EXECUTE</command> can be
3781 used to get around this problem when necessary.
3785 If the same function is used as a trigger for more than one table,
3786 <application>PL/pgSQL</application> prepares and caches plans
3787 independently for each such table — that is, there is a cache
3788 for each trigger function and table combination, not just for each
3789 function. This alleviates some of the problems with varying
3790 data types; for instance, a trigger function will be able to work
3791 successfully with a column named <literal>key</> even if it happens
3792 to have different types in different tables.
3796 Likewise, functions having polymorphic argument types have a separate
3797 plan cache for each combination of actual argument types they have been
3798 invoked for, so that data type differences do not cause unexpected
3803 Plan caching can sometimes have surprising effects on the interpretation
3804 of time-sensitive values. For example there
3805 is a difference between what these two functions do:
3808 CREATE FUNCTION logfunc1(logtxt text) RETURNS void AS $$
3810 INSERT INTO logtable VALUES (logtxt, 'now');
3812 $$ LANGUAGE plpgsql;
3818 CREATE FUNCTION logfunc2(logtxt text) RETURNS void AS $$
3823 INSERT INTO logtable VALUES (logtxt, curtime);
3825 $$ LANGUAGE plpgsql;
3830 In the case of <function>logfunc1</function>, the
3831 <productname>PostgreSQL</productname> main parser knows when
3832 preparing the plan for the <command>INSERT</command> that the
3833 string <literal>'now'</literal> should be interpreted as
3834 <type>timestamp</type>, because the target column of
3835 <classname>logtable</classname> is of that type. Thus,
3836 <literal>'now'</literal> will be converted to a constant when the
3837 <command>INSERT</command> is planned, and then used in all
3838 invocations of <function>logfunc1</function> during the lifetime
3839 of the session. Needless to say, this isn't what the programmer
3844 In the case of <function>logfunc2</function>, the
3845 <productname>PostgreSQL</productname> main parser does not know
3846 what type <literal>'now'</literal> should become and therefore
3847 it returns a data value of type <type>text</type> containing the string
3848 <literal>now</literal>. During the ensuing assignment
3849 to the local variable <varname>curtime</varname>, the
3850 <application>PL/pgSQL</application> interpreter casts this
3851 string to the <type>timestamp</type> type by calling the
3852 <function>text_out</function> and <function>timestamp_in</function>
3853 functions for the conversion. So, the computed time stamp is updated
3854 on each execution as the programmer expects.
3861 <sect1 id="plpgsql-development-tips">
3862 <title>Tips for Developing in <application>PL/pgSQL</application></title>
3865 One good way to develop in
3866 <application>PL/pgSQL</> is to use the text editor of your
3867 choice to create your functions, and in another window, use
3868 <application>psql</application> to load and test those functions.
3869 If you are doing it this way, it
3870 is a good idea to write the function using <command>CREATE OR
3871 REPLACE FUNCTION</>. That way you can just reload the file to update
3872 the function definition. For example:
3874 CREATE OR REPLACE FUNCTION testfunc(integer) RETURNS integer AS $$
3876 $$ LANGUAGE plpgsql;
3881 While running <application>psql</application>, you can load or reload such
3882 a function definition file with:
3886 and then immediately issue SQL commands to test the function.
3890 Another good way to develop in <application>PL/pgSQL</> is with a
3891 GUI database access tool that facilitates development in a
3892 procedural language. One example of such a tool is
3893 <application>pgAdmin</>, although others exist. These tools often
3894 provide convenient features such as escaping single quotes and
3895 making it easier to recreate and debug functions.
3898 <sect2 id="plpgsql-quote-tips">
3899 <title>Handling of Quotation Marks</title>
3902 The code of a <application>PL/pgSQL</> function is specified in
3903 <command>CREATE FUNCTION</command> as a string literal. If you
3904 write the string literal in the ordinary way with surrounding
3905 single quotes, then any single quotes inside the function body
3906 must be doubled; likewise any backslashes must be doubled (assuming
3907 escape string syntax is used).
3908 Doubling quotes is at best tedious, and in more complicated cases
3909 the code can become downright incomprehensible, because you can
3910 easily find yourself needing half a dozen or more adjacent quote marks.
3911 It's recommended that you instead write the function body as a
3912 <quote>dollar-quoted</> string literal (see <xref
3913 linkend="sql-syntax-dollar-quoting">). In the dollar-quoting
3914 approach, you never double any quote marks, but instead take care to
3915 choose a different dollar-quoting delimiter for each level of
3916 nesting you need. For example, you might write the <command>CREATE
3917 FUNCTION</command> command as:
3919 CREATE OR REPLACE FUNCTION testfunc(integer) RETURNS integer AS $PROC$
3921 $PROC$ LANGUAGE plpgsql;
3923 Within this, you might use quote marks for simple literal strings in
3924 SQL commands and <literal>$$</> to delimit fragments of SQL commands
3925 that you are assembling as strings. If you need to quote text that
3926 includes <literal>$$</>, you could use <literal>$Q$</>, and so on.
3930 The following chart shows what you have to do when writing quote
3931 marks without dollar quoting. It might be useful when translating
3932 pre-dollar quoting code into something more comprehensible.
3937 <term>1 quotation mark</term>
3940 To begin and end the function body, for example:
3942 CREATE FUNCTION foo() RETURNS integer AS '
3946 Anywhere within a single-quoted function body, quote marks
3947 <emphasis>must</> appear in pairs.
3953 <term>2 quotation marks</term>
3956 For string literals inside the function body, for example:
3958 a_output := ''Blah'';
3959 SELECT * FROM users WHERE f_name=''foobar'';
3961 In the dollar-quoting approach, you'd just write:
3964 SELECT * FROM users WHERE f_name='foobar';
3966 which is exactly what the <application>PL/pgSQL</> parser would see
3973 <term>4 quotation marks</term>
3976 When you need a single quotation mark in a string constant inside the
3977 function body, for example:
3979 a_output := a_output || '' AND name LIKE ''''foobar'''' AND xyz''
3981 The value actually appended to <literal>a_output</literal> would be:
3982 <literal> AND name LIKE 'foobar' AND xyz</literal>.
3985 In the dollar-quoting approach, you'd write:
3987 a_output := a_output || $$ AND name LIKE 'foobar' AND xyz$$
3989 being careful that any dollar-quote delimiters around this are not
3990 just <literal>$$</>.
3996 <term>6 quotation marks</term>
3999 When a single quotation mark in a string inside the function body is
4000 adjacent to the end of that string constant, for example:
4002 a_output := a_output || '' AND name LIKE ''''foobar''''''
4004 The value appended to <literal>a_output</literal> would then be:
4005 <literal> AND name LIKE 'foobar'</literal>.
4008 In the dollar-quoting approach, this becomes:
4010 a_output := a_output || $$ AND name LIKE 'foobar'$$
4017 <term>10 quotation marks</term>
4020 When you want two single quotation marks in a string constant (which
4021 accounts for 8 quotation marks) and this is adjacent to the end of that
4022 string constant (2 more). You will probably only need that if
4023 you are writing a function that generates other functions, as in
4024 <xref linkend="plpgsql-porting-ex2">.
4027 a_output := a_output || '' if v_'' ||
4028 referrer_keys.kind || '' like ''''''''''
4029 || referrer_keys.key_string || ''''''''''
4030 then return '''''' || referrer_keys.referrer_type
4031 || ''''''; end if;'';
4033 The value of <literal>a_output</literal> would then be:
4035 if v_... like ''...'' then return ''...''; end if;
4039 In the dollar-quoting approach, this becomes:
4041 a_output := a_output || $$ if v_$$ || referrer_keys.kind || $$ like '$$
4042 || referrer_keys.key_string || $$'
4043 then return '$$ || referrer_keys.referrer_type
4046 where we assume we only need to put single quote marks into
4047 <literal>a_output</literal>, because it will be re-quoted before use.
4056 <!-- **** Porting from Oracle PL/SQL **** -->
4058 <sect1 id="plpgsql-porting">
4059 <title>Porting from <productname>Oracle</productname> PL/SQL</title>
4061 <indexterm zone="plpgsql-porting">
4062 <primary>Oracle</primary>
4063 <secondary>porting from PL/SQL to PL/pgSQL</secondary>
4066 <indexterm zone="plpgsql-porting">
4067 <primary>PL/SQL (Oracle)</primary>
4068 <secondary>porting to PL/pgSQL</secondary>
4072 This section explains differences between
4073 <productname>PostgreSQL</>'s <application>PL/pgSQL</application>
4074 language and Oracle's <application>PL/SQL</application> language,
4075 to help developers who port applications from
4076 <trademark class="registered">Oracle</> to <productname>PostgreSQL</>.
4080 <application>PL/pgSQL</application> is similar to PL/SQL in many
4081 aspects. It is a block-structured, imperative language, and all
4082 variables have to be declared. Assignments, loops, conditionals
4083 are similar. The main differences you should keep in mind when
4084 porting from <application>PL/SQL</> to
4085 <application>PL/pgSQL</application> are:
4090 If a name used in a SQL command could be either a column name of a
4091 table or a reference to a variable of the function,
4092 <application>PL/SQL</> treats it as a column name. This corresponds
4093 to <application>PL/pgSQL</>'s
4094 <literal>plpgsql.variable_conflict</> = <literal>use_column</>
4095 behavior, which is not the default,
4096 as explained in <xref linkend="plpgsql-var-subst">.
4097 It's often best to avoid such ambiguities in the first place,
4098 but if you have to port a large amount of code that depends on
4099 this behavior, setting <literal>variable_conflict</> may be the
4106 In <productname>PostgreSQL</> the function body must be written as
4107 a string literal. Therefore you need to use dollar quoting or escape
4108 single quotes in the function body. (See <xref
4109 linkend="plpgsql-quote-tips">.)
4115 Instead of packages, use schemas to organize your functions
4122 Since there are no packages, there are no package-level variables
4123 either. This is somewhat annoying. You can keep per-session state
4124 in temporary tables instead.
4130 Integer <command>FOR</> loops with <literal>REVERSE</> work
4131 differently: <application>PL/SQL</> counts down from the second
4132 number to the first, while <application>PL/pgSQL</> counts down
4133 from the first number to the second, requiring the loop bounds
4134 to be swapped when porting. This incompatibility is unfortunate
4135 but is unlikely to be changed. (See <xref
4136 linkend="plpgsql-integer-for">.)
4142 <command>FOR</> loops over queries (other than cursors) also work
4143 differently: the target variable(s) must have been declared,
4144 whereas <application>PL/SQL</> always declares them implicitly.
4145 An advantage of this is that the variable values are still accessible
4146 after the loop exits.
4152 There are various notational differences for the use of cursor
4161 <title>Porting Examples</title>
4164 <xref linkend="pgsql-porting-ex1"> shows how to port a simple
4165 function from <application>PL/SQL</> to <application>PL/pgSQL</>.
4168 <example id="pgsql-porting-ex1">
4169 <title>Porting a Simple Function from <application>PL/SQL</> to <application>PL/pgSQL</></title>
4172 Here is an <productname>Oracle</productname> <application>PL/SQL</> function:
4174 CREATE OR REPLACE FUNCTION cs_fmt_browser_version(v_name varchar,
4178 IF v_version IS NULL THEN
4181 RETURN v_name || '/' || v_version;
4189 Let's go through this function and see the differences compared to
4190 <application>PL/pgSQL</>:
4195 The <literal>RETURN</literal> key word in the function
4196 prototype (not the function body) becomes
4197 <literal>RETURNS</literal> in
4198 <productname>PostgreSQL</productname>.
4199 Also, <literal>IS</> becomes <literal>AS</>, and you need to
4200 add a <literal>LANGUAGE</> clause because <application>PL/pgSQL</>
4201 is not the only possible function language.
4207 In <productname>PostgreSQL</>, the function body is considered
4208 to be a string literal, so you need to use quote marks or dollar
4209 quotes around it. This substitutes for the terminating <literal>/</>
4210 in the Oracle approach.
4216 The <literal>show errors</literal> command does not exist in
4217 <productname>PostgreSQL</>, and is not needed since errors are
4218 reported automatically.
4225 This is how this function would look when ported to
4226 <productname>PostgreSQL</>:
4229 CREATE OR REPLACE FUNCTION cs_fmt_browser_version(v_name varchar,
4231 RETURNS varchar AS $$
4233 IF v_version IS NULL THEN
4236 RETURN v_name || '/' || v_version;
4238 $$ LANGUAGE plpgsql;
4244 <xref linkend="plpgsql-porting-ex2"> shows how to port a
4245 function that creates another function and how to handle the
4246 ensuing quoting problems.
4249 <example id="plpgsql-porting-ex2">
4250 <title>Porting a Function that Creates Another Function from <application>PL/SQL</> to <application>PL/pgSQL</></title>
4253 The following procedure grabs rows from a
4254 <command>SELECT</command> statement and builds a large function
4255 with the results in <literal>IF</literal> statements, for the
4260 This is the Oracle version:
4262 CREATE OR REPLACE PROCEDURE cs_update_referrer_type_proc IS
4263 CURSOR referrer_keys IS
4264 SELECT * FROM cs_referrer_keys
4266 func_cmd VARCHAR(4000);
4268 func_cmd := 'CREATE OR REPLACE FUNCTION cs_find_referrer_type(v_host IN VARCHAR,
4269 v_domain IN VARCHAR, v_url IN VARCHAR) RETURN VARCHAR IS BEGIN';
4271 FOR referrer_key IN referrer_keys LOOP
4272 func_cmd := func_cmd ||
4273 ' IF v_' || referrer_key.kind
4274 || ' LIKE ''' || referrer_key.key_string
4275 || ''' THEN RETURN ''' || referrer_key.referrer_type
4279 func_cmd := func_cmd || ' RETURN NULL; END;';
4281 EXECUTE IMMEDIATE func_cmd;
4289 Here is how this function would end up in <productname>PostgreSQL</>:
4291 CREATE OR REPLACE FUNCTION cs_update_referrer_type_proc() RETURNS void AS $func$
4293 referrer_keys CURSOR IS
4294 SELECT * FROM cs_referrer_keys
4299 func_body := 'BEGIN';
4301 FOR referrer_key IN referrer_keys LOOP
4302 func_body := func_body ||
4303 ' IF v_' || referrer_key.kind
4304 || ' LIKE ' || quote_literal(referrer_key.key_string)
4305 || ' THEN RETURN ' || quote_literal(referrer_key.referrer_type)
4309 func_body := func_body || ' RETURN NULL; END;';
4312 'CREATE OR REPLACE FUNCTION cs_find_referrer_type(v_host varchar,
4315 RETURNS varchar AS '
4316 || quote_literal(func_body)
4317 || ' LANGUAGE plpgsql;' ;
4321 $func$ LANGUAGE plpgsql;
4323 Notice how the body of the function is built separately and passed
4324 through <literal>quote_literal</> to double any quote marks in it. This
4325 technique is needed because we cannot safely use dollar quoting for
4326 defining the new function: we do not know for sure what strings will
4327 be interpolated from the <structfield>referrer_key.key_string</> field.
4328 (We are assuming here that <structfield>referrer_key.kind</> can be
4329 trusted to always be <literal>host</>, <literal>domain</>, or
4330 <literal>url</>, but <structfield>referrer_key.key_string</> might be
4331 anything, in particular it might contain dollar signs.) This function
4332 is actually an improvement on the Oracle original, because it will
4333 not generate broken code when <structfield>referrer_key.key_string</> or
4334 <structfield>referrer_key.referrer_type</> contain quote marks.
4339 <xref linkend="plpgsql-porting-ex3"> shows how to port a function
4340 with <literal>OUT</> parameters and string manipulation.
4341 <productname>PostgreSQL</> does not have a built-in
4342 <function>instr</function> function, but you can create one
4343 using a combination of other
4344 functions.<indexterm><primary>instr</></indexterm> In <xref
4345 linkend="plpgsql-porting-appendix"> there is a
4346 <application>PL/pgSQL</application> implementation of
4347 <function>instr</function> that you can use to make your porting
4351 <example id="plpgsql-porting-ex3">
4352 <title>Porting a Procedure With String Manipulation and
4353 <literal>OUT</> Parameters from <application>PL/SQL</> to
4354 <application>PL/pgSQL</></title>
4357 The following <productname>Oracle</productname> PL/SQL procedure is used
4358 to parse a URL and return several elements (host, path, and query).
4362 This is the Oracle version:
4364 CREATE OR REPLACE PROCEDURE cs_parse_url(
4366 v_host OUT VARCHAR, -- This will be passed back
4367 v_path OUT VARCHAR, -- This one too
4368 v_query OUT VARCHAR) -- And this one
4376 a_pos1 := instr(v_url, '//');
4381 a_pos2 := instr(v_url, '/', a_pos1 + 2);
4383 v_host := substr(v_url, a_pos1 + 2);
4388 v_host := substr(v_url, a_pos1 + 2, a_pos2 - a_pos1 - 2);
4389 a_pos1 := instr(v_url, '?', a_pos2 + 1);
4392 v_path := substr(v_url, a_pos2);
4396 v_path := substr(v_url, a_pos2, a_pos1 - a_pos2);
4397 v_query := substr(v_url, a_pos1 + 1);
4405 Here is a possible translation into <application>PL/pgSQL</>:
4407 CREATE OR REPLACE FUNCTION cs_parse_url(
4409 v_host OUT VARCHAR, -- This will be passed back
4410 v_path OUT VARCHAR, -- This one too
4411 v_query OUT VARCHAR) -- And this one
4420 a_pos1 := instr(v_url, '//');
4425 a_pos2 := instr(v_url, '/', a_pos1 + 2);
4427 v_host := substr(v_url, a_pos1 + 2);
4432 v_host := substr(v_url, a_pos1 + 2, a_pos2 - a_pos1 - 2);
4433 a_pos1 := instr(v_url, '?', a_pos2 + 1);
4436 v_path := substr(v_url, a_pos2);
4440 v_path := substr(v_url, a_pos2, a_pos1 - a_pos2);
4441 v_query := substr(v_url, a_pos1 + 1);
4443 $$ LANGUAGE plpgsql;
4446 This function could be used like this:
4448 SELECT * FROM cs_parse_url('http://foobar.com/query.cgi?baz');
4454 <xref linkend="plpgsql-porting-ex4"> shows how to port a procedure
4455 that uses numerous features that are specific to Oracle.
4458 <example id="plpgsql-porting-ex4">
4459 <title>Porting a Procedure from <application>PL/SQL</> to <application>PL/pgSQL</></title>
4465 CREATE OR REPLACE PROCEDURE cs_create_job(v_job_id IN INTEGER) IS
4466 a_running_job_count INTEGER;
4467 PRAGMA AUTONOMOUS_TRANSACTION;<co id="co.plpgsql-porting-pragma">
4469 LOCK TABLE cs_jobs IN EXCLUSIVE MODE;<co id="co.plpgsql-porting-locktable">
4471 SELECT count(*) INTO a_running_job_count FROM cs_jobs WHERE end_stamp IS NULL;
4473 IF a_running_job_count > 0 THEN
4474 COMMIT; -- free lock<co id="co.plpgsql-porting-commit">
4475 raise_application_error(-20000,
4476 'Unable to create a new job: a job is currently running.');
4479 DELETE FROM cs_active_job;
4480 INSERT INTO cs_active_job(job_id) VALUES (v_job_id);
4483 INSERT INTO cs_jobs (job_id, start_stamp) VALUES (v_job_id, sysdate);
4485 WHEN dup_val_on_index THEN NULL; -- don't worry if it already exists
4495 Procedures like this can easily be converted into <productname>PostgreSQL</>
4496 functions returning <type>void</type>. This procedure in
4497 particular is interesting because it can teach us some things:
4500 <callout arearefs="co.plpgsql-porting-pragma">
4502 There is no <literal>PRAGMA</literal> statement in <productname>PostgreSQL</>.
4506 <callout arearefs="co.plpgsql-porting-locktable">
4508 If you do a <command>LOCK TABLE</command> in <application>PL/pgSQL</>,
4509 the lock will not be released until the calling transaction is
4514 <callout arearefs="co.plpgsql-porting-commit">
4516 You cannot issue <command>COMMIT</> in a
4517 <application>PL/pgSQL</application> function. The function is
4518 running within some outer transaction and so <command>COMMIT</>
4519 would imply terminating the function's execution. However, in
4520 this particular case it is not necessary anyway, because the lock
4521 obtained by the <command>LOCK TABLE</command> will be released when
4529 This is how we could port this procedure to <application>PL/pgSQL</>:
4532 CREATE OR REPLACE FUNCTION cs_create_job(v_job_id integer) RETURNS void AS $$
4534 a_running_job_count integer;
4536 LOCK TABLE cs_jobs IN EXCLUSIVE MODE;
4538 SELECT count(*) INTO a_running_job_count FROM cs_jobs WHERE end_stamp IS NULL;
4540 IF a_running_job_count > 0 THEN
4541 RAISE EXCEPTION 'Unable to create a new job: a job is currently running';<co id="co.plpgsql-porting-raise">
4544 DELETE FROM cs_active_job;
4545 INSERT INTO cs_active_job(job_id) VALUES (v_job_id);
4548 INSERT INTO cs_jobs (job_id, start_stamp) VALUES (v_job_id, now());
4550 WHEN unique_violation THEN <co id="co.plpgsql-porting-exception">
4551 -- don't worry if it already exists
4554 $$ LANGUAGE plpgsql;
4558 <callout arearefs="co.plpgsql-porting-raise">
4560 The syntax of <literal>RAISE</> is considerably different from
4561 Oracle's statement, although the basic case <literal>RAISE</>
4562 <replaceable class="parameter">exception_name</replaceable> works
4566 <callout arearefs="co.plpgsql-porting-exception">
4568 The exception names supported by <application>PL/pgSQL</> are
4569 different from Oracle's. The set of built-in exception names
4570 is much larger (see <xref linkend="errcodes-appendix">). There
4571 is not currently a way to declare user-defined exception names,
4572 although you can throw user-chosen SQLSTATE values instead.
4577 The main functional difference between this procedure and the
4578 Oracle equivalent is that the exclusive lock on the <literal>cs_jobs</>
4579 table will be held until the calling transaction completes. Also, if
4580 the caller later aborts (for example due to an error), the effects of
4581 this procedure will be rolled back.
4586 <sect2 id="plpgsql-porting-other">
4587 <title>Other Things to Watch For</title>
4590 This section explains a few other things to watch for when porting
4591 Oracle <application>PL/SQL</> functions to
4592 <productname>PostgreSQL</productname>.
4595 <sect3 id="plpgsql-porting-exceptions">
4596 <title>Implicit Rollback after Exceptions</title>
4599 In <application>PL/pgSQL</>, when an exception is caught by an
4600 <literal>EXCEPTION</> clause, all database changes since the block's
4601 <literal>BEGIN</> are automatically rolled back. That is, the behavior
4602 is equivalent to what you'd get in Oracle with:
4618 If you are translating an Oracle procedure that uses
4619 <command>SAVEPOINT</> and <command>ROLLBACK TO</> in this style,
4620 your task is easy: just omit the <command>SAVEPOINT</> and
4621 <command>ROLLBACK TO</>. If you have a procedure that uses
4622 <command>SAVEPOINT</> and <command>ROLLBACK TO</> in a different way
4623 then some actual thought will be required.
4628 <title><command>EXECUTE</command></title>
4631 The <application>PL/pgSQL</> version of
4632 <command>EXECUTE</command> works similarly to the
4633 <application>PL/SQL</> version, but you have to remember to use
4634 <function>quote_literal</function> and
4635 <function>quote_ident</function> as described in <xref
4636 linkend="plpgsql-statements-executing-dyn">. Constructs of the
4637 type <literal>EXECUTE 'SELECT * FROM $1';</literal> will not work
4638 reliably unless you use these functions.
4642 <sect3 id="plpgsql-porting-optimization">
4643 <title>Optimizing <application>PL/pgSQL</application> Functions</title>
4646 <productname>PostgreSQL</> gives you two function creation
4647 modifiers to optimize execution: <quote>volatility</> (whether
4648 the function always returns the same result when given the same
4649 arguments) and <quote>strictness</quote> (whether the function
4650 returns null if any argument is null). Consult the <xref
4651 linkend="sql-createfunction">
4652 reference page for details.
4656 When making use of these optimization attributes, your
4657 <command>CREATE FUNCTION</command> statement might look something
4661 CREATE FUNCTION foo(...) RETURNS integer AS $$
4663 $$ LANGUAGE plpgsql STRICT IMMUTABLE;
4669 <sect2 id="plpgsql-porting-appendix">
4670 <title>Appendix</title>
4673 This section contains the code for a set of Oracle-compatible
4674 <function>instr</function> functions that you can use to simplify
4675 your porting efforts.
4680 -- instr functions that mimic Oracle's counterpart
4681 -- Syntax: instr(string1, string2, [n], [m]) where [] denotes optional parameters.
4683 -- Searches string1 beginning at the nth character for the mth occurrence
4684 -- of string2. If n is negative, search backwards. If m is not passed,
4685 -- assume 1 (search starts at first character).
4688 CREATE FUNCTION instr(varchar, varchar) RETURNS integer AS $$
4692 pos:= instr($1, $2, 1);
4695 $$ LANGUAGE plpgsql STRICT IMMUTABLE;
4698 CREATE FUNCTION instr(string varchar, string_to_search varchar, beg_index integer)
4699 RETURNS integer AS $$
4701 pos integer NOT NULL DEFAULT 0;
4707 IF beg_index > 0 THEN
4708 temp_str := substring(string FROM beg_index);
4709 pos := position(string_to_search IN temp_str);
4714 RETURN pos + beg_index - 1;
4717 ss_length := char_length(string_to_search);
4718 length := char_length(string);
4719 beg := length + beg_index - ss_length + 2;
4721 WHILE beg > 0 LOOP
4722 temp_str := substring(string FROM beg FOR ss_length);
4723 pos := position(string_to_search IN temp_str);
4735 $$ LANGUAGE plpgsql STRICT IMMUTABLE;
4738 CREATE FUNCTION instr(string varchar, string_to_search varchar,
4739 beg_index integer, occur_index integer)
4740 RETURNS integer AS $$
4742 pos integer NOT NULL DEFAULT 0;
4743 occur_number integer NOT NULL DEFAULT 0;
4750 IF beg_index > 0 THEN
4752 temp_str := substring(string FROM beg_index);
4754 FOR i IN 1..occur_index LOOP
4755 pos := position(string_to_search IN temp_str);
4758 beg := beg + pos - 1;
4763 temp_str := substring(string FROM beg + 1);
4772 ss_length := char_length(string_to_search);
4773 length := char_length(string);
4774 beg := length + beg_index - ss_length + 2;
4776 WHILE beg > 0 LOOP
4777 temp_str := substring(string FROM beg FOR ss_length);
4778 pos := position(string_to_search IN temp_str);
4781 occur_number := occur_number + 1;
4783 IF occur_number = occur_index THEN
4794 $$ LANGUAGE plpgsql STRICT IMMUTABLE;