1 <!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.137 2009/02/04 21:30:41 alvherre Exp $ -->
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.
61 <sect2 id="plpgsql-advantages">
62 <title>Advantages of Using <application>PL/pgSQL</application></title>
65 <acronym>SQL</acronym> is the language <productname>PostgreSQL</>
66 and most other relational databases use as query language. It's
67 portable and easy to learn. But every <acronym>SQL</acronym>
68 statement must be executed individually by the database server.
72 That means that your client application must send each query to
73 the database server, wait for it to be processed, receive and
74 process the results, do some computation, then send further
75 queries to the server. All this incurs interprocess
76 communication and will also incur network overhead if your client
77 is on a different machine than the database server.
81 With <application>PL/pgSQL</application> you can group a block of
82 computation and a series of queries <emphasis>inside</emphasis>
83 the database server, thus having the power of a procedural
84 language and the ease of use of SQL, but with considerable
85 savings of client/server communication overhead.
89 <listitem><para> Extra round trips between
90 client and server are eliminated </para></listitem>
92 <listitem><para> Intermediate results that the client does not
93 need do not have to be marshaled or transferred between server
94 and client </para></listitem>
96 <listitem><para> Multiple rounds of query
97 parsing can be avoided </para></listitem>
100 <para> This can result in a considerable performance increase as
101 compared to an application that does not use stored functions.
105 Also, with <application>PL/pgSQL</application> you can use all
106 the data types, operators and functions of SQL.
110 <sect2 id="plpgsql-args-results">
111 <title>Supported Argument and Result Data Types</title>
114 Functions written in <application>PL/pgSQL</application> can accept
115 as arguments any scalar or array data type supported by the server,
116 and they can return a result of any of these types. They can also
117 accept or return any composite type (row type) specified by name.
118 It is also possible to declare a <application>PL/pgSQL</application>
119 function as returning <type>record</>, which means that the result
120 is a row type whose columns are determined by specification in the
121 calling query, as discussed in <xref linkend="queries-tablefunctions">.
125 <application>PL/pgSQL</> functions can be declared to accept a variable
126 number of arguments by using the <literal>VARIADIC</> marker. This
127 works exactly the same way as for SQL functions, as discussed in
128 <xref linkend="xfunc-sql-variadic-functions">.
132 <application>PL/pgSQL</> functions can also be declared to accept
133 and return the polymorphic types
134 <type>anyelement</type>, <type>anyarray</type>, <type>anynonarray</type>,
135 and <type>anyenum</>. The actual
136 data types handled by a polymorphic function can vary from call to
137 call, as discussed in <xref linkend="extend-types-polymorphic">.
138 An example is shown in <xref linkend="plpgsql-declaration-aliases">.
142 <application>PL/pgSQL</> functions can also be declared to return
143 a <quote>set</> (or table) of any data type that can be returned as
144 a single instance. Such a function generates its output by executing
145 <command>RETURN NEXT</> for each desired element of the result
146 set, or by using <command>RETURN QUERY</> to output the result of
151 Finally, a <application>PL/pgSQL</> function can be declared to return
152 <type>void</> if it has no useful return value.
156 <application>PL/pgSQL</> functions can also be declared with output
157 parameters in place of an explicit specification of the return type.
158 This does not add any fundamental capability to the language, but
159 it is often convenient, especially for returning multiple values.
160 The <literal>RETURNS TABLE</> notation can also be used in place
161 of <literal>RETURNS SETOF</>.
165 Specific examples appear in
166 <xref linkend="plpgsql-declaration-aliases"> and
167 <xref linkend="plpgsql-statements-returning">.
172 <sect1 id="plpgsql-structure">
173 <title>Structure of <application>PL/pgSQL</application></title>
176 <application>PL/pgSQL</application> is a block-structured language.
177 The complete text of a function definition must be a
178 <firstterm>block</>. A block is defined as:
181 <optional> <<<replaceable>label</replaceable>>> </optional>
183 <replaceable>declarations</replaceable> </optional>
185 <replaceable>statements</replaceable>
186 END <optional> <replaceable>label</replaceable> </optional>;
191 Each declaration and each statement within a block is terminated
192 by a semicolon. A block that appears within another block must
193 have a semicolon after <literal>END</literal>, as shown above;
194 however the final <literal>END</literal> that
195 concludes a function body does not require a semicolon.
200 A common mistake is to write a semicolon immediately after
201 <literal>BEGIN</>. This is incorrect and will result in a syntax error.
206 A <replaceable>label</replaceable> is only needed if you want to
207 identify the block for use
208 in an <literal>EXIT</> statement, or to qualify the names of the
209 variables declared in the block. If a label is given after
210 <literal>END</>, it must match the label at the block's beginning.
214 All key words are case-insensitive.
215 Identifiers are implicitly converted to lowercase
216 unless double-quoted, just as they are in ordinary SQL commands.
220 There are two types of comments in <application>PL/pgSQL</>. A double
221 dash (<literal>--</literal>) starts a comment that extends to the end of
222 the line. A <literal>/*</literal> starts a block comment that extends to
223 the next occurrence of <literal>*/</literal>. Block comments cannot be
224 nested, but double dash comments can be enclosed into a block comment and
225 a double dash can hide the block comment delimiters <literal>/*</literal>
226 and <literal>*/</literal>.
230 Any statement in the statement section of a block
231 can be a <firstterm>subblock</>. Subblocks can be used for
232 logical grouping or to localize variables to a small group
233 of statements. Variables declared in a subblock mask any
234 similarly-named variables of outer blocks for the duration
235 of the subblock; but you can access the outer variables anyway
236 if you qualify their names with their block's label. For example:
238 CREATE FUNCTION somefunc() RETURNS integer AS $$
239 << outerblock >>
241 quantity integer := 30;
243 RAISE NOTICE 'Quantity here is %', quantity; -- Prints 30
249 quantity integer := 80;
251 RAISE NOTICE 'Quantity here is %', quantity; -- Prints 80
252 RAISE NOTICE 'Outer quantity here is %', outerblock.quantity; -- Prints 50
255 RAISE NOTICE 'Quantity here is %', quantity; -- Prints 50
265 There is actually a hidden <quote>outer block</> surrounding the body
266 of any <application>PL/pgSQL</> function. This block provides the
267 declarations of the function's parameters (if any), as well as some
268 special variables such as <literal>FOUND</literal> (see
269 <xref linkend="plpgsql-statements-diagnostics">). The outer block is
270 labeled with the function's name, meaning that parameters and special
271 variables can be qualified with the function's name.
276 It is important not to confuse the use of
277 <command>BEGIN</>/<command>END</> for grouping statements in
278 <application>PL/pgSQL</> with the similarly-named SQL commands
280 control. <application>PL/pgSQL</>'s <command>BEGIN</>/<command>END</>
281 are only for grouping; they do not start or end a transaction.
282 Functions and trigger procedures are always executed within a transaction
283 established by an outer query — they cannot start or commit that
284 transaction, since there would be no context for them to execute in.
285 However, a block containing an <literal>EXCEPTION</> clause effectively
286 forms a subtransaction that can be rolled back without affecting the
287 outer transaction. For more about that see <xref
288 linkend="plpgsql-error-trapping">.
292 <sect1 id="plpgsql-declarations">
293 <title>Declarations</title>
296 All variables used in a block must be declared in the
297 declarations section of the block.
298 (The only exceptions are that the loop variable of a <literal>FOR</> loop
299 iterating over a range of integer values is automatically declared as an
300 integer variable, and likewise the loop variable of a <literal>FOR</> loop
301 iterating over a cursor's result is automatically declared as a
306 <application>PL/pgSQL</> variables can have any SQL data type, such as
307 <type>integer</type>, <type>varchar</type>, and
312 Here are some examples of variable declarations:
317 myrow tablename%ROWTYPE;
318 myfield tablename.columnname%TYPE;
324 The general syntax of a variable declaration is:
326 <replaceable>name</replaceable> <optional> CONSTANT </optional> <replaceable>type</replaceable> <optional> NOT NULL </optional> <optional> { DEFAULT | := } <replaceable>expression</replaceable> </optional>;
328 The <literal>DEFAULT</> clause, if given, specifies the initial value assigned
329 to the variable when the block is entered. If the <literal>DEFAULT</> clause
330 is not given then the variable is initialized to the
331 <acronym>SQL</acronym> null value.
332 The <literal>CONSTANT</> option prevents the variable from being assigned to,
333 so that its value remains constant for the duration of the block.
334 If <literal>NOT NULL</>
335 is specified, an assignment of a null value results in a run-time
336 error. All variables declared as <literal>NOT NULL</>
337 must have a nonnull default value specified.
341 A variable's default value is evaluated and assigned to the variable
342 each time the block is entered (not just once per function call).
343 So, for example, assigning <literal>now()</literal> to a variable of type
344 <type>timestamp</type> causes the variable to have the
345 time of the current function call, not the time when the function was
352 quantity integer DEFAULT 32;
353 url varchar := 'http://mysite.com';
354 user_id CONSTANT integer := 10;
358 <sect2 id="plpgsql-declaration-aliases">
359 <title>Aliases for Function Parameters</title>
362 Parameters passed to functions are named with the identifiers
363 <literal>$1</literal>, <literal>$2</literal>,
364 etc. Optionally, aliases can be declared for
365 <literal>$<replaceable>n</replaceable></literal>
366 parameter names for increased readability. Either the alias or the
367 numeric identifier can then be used to refer to the parameter value.
371 There are two ways to create an alias. The preferred way is to give a
372 name to the parameter in the <command>CREATE FUNCTION</command> command,
375 CREATE FUNCTION sales_tax(subtotal real) RETURNS real AS $$
377 RETURN subtotal * 0.06;
381 The other way, which was the only way available before
382 <productname>PostgreSQL</productname> 8.0, is to explicitly
383 declare an alias, using the declaration syntax
386 <replaceable>name</replaceable> ALIAS FOR $<replaceable>n</replaceable>;
389 The same example in this style looks like:
391 CREATE FUNCTION sales_tax(real) RETURNS real AS $$
393 subtotal ALIAS FOR $1;
395 RETURN subtotal * 0.06;
403 These two examples are not perfectly equivalent. In the first case,
404 <literal>subtotal</> could be referenced as
405 <literal>sales_tax.subtotal</>, but in the second case it could not.
406 (Had we attached a label to the block, <literal>subtotal</> could
407 be qualified with that label, instead.)
414 CREATE FUNCTION instr(varchar, integer) RETURNS integer AS $$
416 v_string ALIAS FOR $1;
419 -- some computations using v_string and index here
424 CREATE FUNCTION concat_selected_fields(in_t sometablename) RETURNS text AS $$
426 RETURN in_t.f1 || in_t.f3 || in_t.f5 || in_t.f7;
433 When a <application>PL/pgSQL</application> function is declared
434 with output parameters, the output parameters are given
435 <literal>$<replaceable>n</replaceable></literal> names and optional
436 aliases in just the same way as the normal input parameters. An
437 output parameter is effectively a variable that starts out NULL;
438 it should be assigned to during the execution of the function.
439 The final value of the parameter is what is returned. For instance,
440 the sales-tax example could also be done this way:
443 CREATE FUNCTION sales_tax(subtotal real, OUT tax real) AS $$
445 tax := subtotal * 0.06;
450 Notice that we omitted <literal>RETURNS real</> — we could have
451 included it, but it would be redundant.
455 Output parameters are most useful when returning multiple values.
456 A trivial example is:
459 CREATE FUNCTION sum_n_product(x int, y int, OUT sum int, OUT prod int) AS $$
467 As discussed in <xref linkend="xfunc-output-parameters">, this
468 effectively creates an anonymous record type for the function's
469 results. If a <literal>RETURNS</> clause is given, it must say
470 <literal>RETURNS record</>.
474 Another way to declare a <application>PL/pgSQL</application> function
475 is with <literal>RETURNS TABLE</>, for example:
478 CREATE FUNCTION extended_sales(p_itemno int) RETURNS TABLE(quantity int, total numeric) AS $$
480 RETURN QUERY SELECT quantity, quantity * price FROM sales WHERE itemno = p_itemno;
485 This is exactly equivalent to declaring one or more <literal>OUT</>
486 parameters and specifying <literal>RETURNS SETOF
487 <replaceable>sometype</></literal>.
491 When the return type of a <application>PL/pgSQL</application>
492 function is declared as a polymorphic type (<type>anyelement</type>,
493 <type>anyarray</type>, <type>anynonarray</type>, or <type>anyenum</>),
494 a special parameter <literal>$0</literal>
495 is created. Its data type is the actual return type of the function,
496 as deduced from the actual input types (see <xref
497 linkend="extend-types-polymorphic">).
498 This allows the function to access its actual return type
499 as shown in <xref linkend="plpgsql-declaration-type">.
500 <literal>$0</literal> is initialized to null and can be modified by
501 the function, so it can be used to hold the return value if desired,
502 though that is not required. <literal>$0</literal> can also be
503 given an alias. For example, this function works on any data type
504 that has a <literal>+</> operator:
507 CREATE FUNCTION add_three_values(v1 anyelement, v2 anyelement, v3 anyelement)
508 RETURNS anyelement AS $$
512 result := v1 + v2 + v3;
520 The same effect can be had by declaring one or more output parameters as
521 polymorphic types. In this case the
522 special <literal>$0</literal> parameter is not used; the output
523 parameters themselves serve the same purpose. For example:
526 CREATE FUNCTION add_three_values(v1 anyelement, v2 anyelement, v3 anyelement,
537 <sect2 id="plpgsql-declaration-type">
538 <title>Copying Types</title>
541 <replaceable>variable</replaceable>%TYPE
545 <literal>%TYPE</literal> provides the data type of a variable or
546 table column. You can use this to declare variables that will hold
547 database values. For example, let's say you have a column named
548 <literal>user_id</literal> in your <literal>users</literal>
549 table. To declare a variable with the same data type as
550 <literal>users.user_id</> you write:
552 user_id users.user_id%TYPE;
557 By using <literal>%TYPE</literal> you don't need to know the data
558 type of the structure you are referencing, and most importantly,
559 if the data type of the referenced item changes in the future (for
560 instance: you change the type of <literal>user_id</>
561 from <type>integer</type> to <type>real</type>), you might not need
562 to change your function definition.
566 <literal>%TYPE</literal> is particularly valuable in polymorphic
567 functions, since the data types needed for internal variables can
568 change from one call to the next. Appropriate variables can be
569 created by applying <literal>%TYPE</literal> to the function's
570 arguments or result placeholders.
575 <sect2 id="plpgsql-declaration-rowtypes">
576 <title>Row Types</title>
579 <replaceable>name</replaceable> <replaceable>table_name</replaceable><literal>%ROWTYPE</literal>;
580 <replaceable>name</replaceable> <replaceable>composite_type_name</replaceable>;
584 A variable of a composite type is called a <firstterm>row</>
585 variable (or <firstterm>row-type</> variable). Such a variable
586 can hold a whole row of a <command>SELECT</> or <command>FOR</>
587 query result, so long as that query's column set matches the
588 declared type of the variable.
589 The individual fields of the row value
590 are accessed using the usual dot notation, for example
591 <literal>rowvar.field</literal>.
595 A row variable can be declared to have the same type as the rows of
596 an existing table or view, by using the
597 <replaceable>table_name</replaceable><literal>%ROWTYPE</literal>
598 notation; or it can be declared by giving a composite type's name.
599 (Since every table has an associated composite type of the same name,
600 it actually does not matter in <productname>PostgreSQL</> whether you
601 write <literal>%ROWTYPE</literal> or not. But the form with
602 <literal>%ROWTYPE</literal> is more portable.)
606 Parameters to a function can be
607 composite types (complete table rows). In that case, the
608 corresponding identifier <literal>$<replaceable>n</replaceable></> will be a row variable, and fields can
609 be selected from it, for example <literal>$1.user_id</literal>.
613 Only the user-defined columns of a table row are accessible in a
614 row-type variable, not the OID or other system columns (because the
615 row could be from a view). The fields of the row type inherit the
616 table's field size or precision for data types such as
617 <type>char(<replaceable>n</>)</type>.
621 Here is an example of using composite types. <structname>table1</>
622 and <structname>table2</> are existing tables having at least the
626 CREATE FUNCTION merge_fields(t_row table1) RETURNS text AS $$
628 t2_row table2%ROWTYPE;
630 SELECT * INTO t2_row FROM table2 WHERE ... ;
631 RETURN t_row.f1 || t2_row.f3 || t_row.f5 || t2_row.f7;
635 SELECT merge_fields(t.*) FROM table1 t WHERE ... ;
640 <sect2 id="plpgsql-declaration-records">
641 <title>Record Types</title>
644 <replaceable>name</replaceable> RECORD;
648 Record variables are similar to row-type variables, but they have no
649 predefined structure. They take on the actual row structure of the
650 row they are assigned during a <command>SELECT</> or <command>FOR</> command. The substructure
651 of a record variable can change each time it is assigned to.
652 A consequence of this is that until a record variable is first assigned
653 to, it has no substructure, and any attempt to access a
654 field in it will draw a run-time error.
658 Note that <literal>RECORD</> is not a true data type, only a placeholder.
659 One should also realize that when a <application>PL/pgSQL</application>
660 function is declared to return type <type>record</>, this is not quite the
661 same concept as a record variable, even though such a function might
662 use a record variable to hold its result. In both cases the actual row
663 structure is unknown when the function is written, but for a function
664 returning <type>record</> the actual structure is determined when the
665 calling query is parsed, whereas a record variable can change its row
666 structure on-the-fly.
670 <sect2 id="plpgsql-declaration-renaming-vars">
671 <title><literal>RENAME</></title>
674 RENAME <replaceable>oldname</replaceable> TO <replaceable>newname</replaceable>;
678 Using the <literal>RENAME</literal> declaration you can change the
679 name of a variable, record or row. This is primarily useful if
680 <varname>NEW</varname> or <varname>OLD</varname> should be
681 referenced by another name inside a trigger procedure. See also
682 <literal>ALIAS</literal>.
688 RENAME id TO user_id;
689 RENAME this_var TO that_var;
695 <literal>RENAME</literal> appears to be broken as of
696 <productname>PostgreSQL</> 7.3. Fixing this is of low priority,
697 since <literal>ALIAS</literal> covers most of the practical uses
698 of <literal>RENAME</literal>.
704 <sect1 id="plpgsql-expressions">
705 <title>Expressions</title>
708 All expressions used in <application>PL/pgSQL</application>
709 statements are processed using the server's main
710 <acronym>SQL</acronym> executor. For example, when you write
711 a <application>PL/pgSQL</application> statement like
713 IF <replaceable>expression</replaceable> THEN ...
715 <application>PL/pgSQL</application> will evaluate the expression by
718 SELECT <replaceable>expression</replaceable>
720 to the main SQL engine. While forming the <command>SELECT</> command,
721 any occurrences of <application>PL/pgSQL</application> variable names
722 are replaced by parameters, as discussed in detail in
723 <xref linkend="plpgsql-var-subst">.
724 This allows the query plan for the <command>SELECT</command> to
725 be prepared just once and then reused for subsequent
726 evaluations with different values of the variables. Thus, what
727 really happens on first use of an expression is essentially a
728 <command>PREPARE</> command. For example, if we have declared
729 two integer variables <literal>x</> and <literal>y</>, and we write
733 what happens behind the scenes is
735 PREPARE <replaceable>statement_name</>(integer, integer) AS SELECT $1 < $2;
737 and then this prepared statement is <command>EXECUTE</>d for each
738 execution of the <command>IF</> statement, with the current values
739 of the <application>PL/pgSQL</application> variables supplied as
741 The query plan prepared in this way is saved for the life of the database
742 connection, as described in
743 <xref linkend="plpgsql-plan-caching">. Normally these details are
744 not important to a <application>PL/pgSQL</application> user, but
745 they are useful to know when trying to diagnose a problem.
749 <sect1 id="plpgsql-statements">
750 <title>Basic Statements</title>
753 In this section and the following ones, we describe all the statement
754 types that are explicitly understood by
755 <application>PL/pgSQL</application>.
756 Anything not recognized as one of these statement types is presumed
757 to be an SQL command and is sent to the main database engine to execute,
758 as described in <xref linkend="plpgsql-statements-sql-noresult">
759 and <xref linkend="plpgsql-statements-sql-onerow">.
762 <sect2 id="plpgsql-statements-assignment">
763 <title>Assignment</title>
766 An assignment of a value to a <application>PL/pgSQL</application>
767 variable or row/record field is written as:
769 <replaceable>variable</replaceable> := <replaceable>expression</replaceable>;
771 As explained above, the expression in such a statement is evaluated
772 by means of an SQL <command>SELECT</> command sent to the main
773 database engine. The expression must yield a single value.
777 If the expression's result data type doesn't match the variable's
778 data type, or the variable has a specific size/precision
779 (like <type>char(20)</type>), the result value will be implicitly
780 converted by the <application>PL/pgSQL</application> interpreter using
781 the result type's output-function and
782 the variable type's input-function. Note that this could potentially
783 result in run-time errors generated by the input function, if the
784 string form of the result value is not acceptable to the input function.
790 tax := subtotal * 0.06;
791 my_record.user_id := 20;
796 <sect2 id="plpgsql-statements-sql-noresult">
797 <title>Executing a Command With No Result</title>
800 For any SQL command that does not return rows, for example
801 <command>INSERT</> without a <literal>RETURNING</> clause, you can
802 execute the command within a <application>PL/pgSQL</application> function
803 just by writing the command.
807 Any <application>PL/pgSQL</application> variable name appearing
808 in the command text is replaced by a parameter symbol, and then the
809 current value of the variable is provided as the parameter value
810 at run time. This is exactly like the processing described earlier
811 for expressions; for details see <xref linkend="plpgsql-var-subst">.
812 As an example, if you write:
819 UPDATE mytab SET val = val + delta WHERE id = key;
821 the command text seen by the main SQL engine will look like:
823 UPDATE mytab SET val = val + $1 WHERE id = $2;
825 Although you don't normally have to think about this, it's helpful
826 to know it when you need to make sense of syntax-error messages.
831 <application>PL/pgSQL</application> will substitute for any identifier
832 matching one of the function's declared variables; it is not bright
833 enough to know whether that's what you meant! Thus, it is a bad idea
834 to use a variable name that is the same as any table, column, or
835 function name that you need to reference in commands within the
836 function. For more discussion see <xref linkend="plpgsql-var-subst">.
841 When executing a SQL command in this way,
842 <application>PL/pgSQL</application> plans the command just once
843 and re-uses the plan on subsequent executions, for the life of
844 the database connection. The implications of this are discussed
845 in detail in <xref linkend="plpgsql-plan-caching">.
849 Sometimes it is useful to evaluate an expression or <command>SELECT</>
850 query but discard the result, for example when calling a function
851 that has side-effects but no useful result value. To do
852 this in <application>PL/pgSQL</application>, use the
853 <command>PERFORM</command> statement:
856 PERFORM <replaceable>query</replaceable>;
859 This executes <replaceable>query</replaceable> and discards the
860 result. Write the <replaceable>query</replaceable> the same
861 way you would write an SQL <command>SELECT</> command, but replace the
862 initial keyword <command>SELECT</> with <command>PERFORM</command>.
863 <application>PL/pgSQL</application> variables will be
864 substituted into the query just as for commands that return no result,
865 and the plan is cached in the same way. Also, the special variable
866 <literal>FOUND</literal> is set to true if the query produced at
867 least one row, or false if it produced no rows (see
868 <xref linkend="plpgsql-statements-diagnostics">).
873 One might expect that writing <command>SELECT</command> directly
874 would accomplish this result, but at
875 present the only accepted way to do it is
876 <command>PERFORM</command>. A SQL command that can return rows,
877 such as <command>SELECT</command>, will be rejected as an error
878 unless it has an <literal>INTO</> clause as discussed in the
886 PERFORM create_mv('cs_session_page_requests_mv', my_query);
891 <sect2 id="plpgsql-statements-sql-onerow">
892 <title>Executing a Query with a Single-Row Result</title>
894 <indexterm zone="plpgsql-statements-sql-onerow">
895 <primary>SELECT INTO</primary>
896 <secondary>in PL/pgSQL</secondary>
899 <indexterm zone="plpgsql-statements-sql-onerow">
900 <primary>RETURNING INTO</primary>
901 <secondary>in PL/pgSQL</secondary>
905 The result of a SQL command yielding a single row (possibly of multiple
906 columns) can be assigned to a record variable, row-type variable, or list
907 of scalar variables. This is done by writing the base SQL command and
908 adding an <literal>INTO</> clause. For example,
911 SELECT <replaceable>select_expressions</replaceable> INTO <optional>STRICT</optional> <replaceable>target</replaceable> FROM ...;
912 INSERT ... RETURNING <replaceable>expressions</replaceable> INTO <optional>STRICT</optional> <replaceable>target</replaceable>;
913 UPDATE ... RETURNING <replaceable>expressions</replaceable> INTO <optional>STRICT</optional> <replaceable>target</replaceable>;
914 DELETE ... RETURNING <replaceable>expressions</replaceable> INTO <optional>STRICT</optional> <replaceable>target</replaceable>;
917 where <replaceable>target</replaceable> can be a record variable, a row
918 variable, or a comma-separated list of simple variables and
920 <application>PL/pgSQL</application> variables will be
921 substituted into the rest of the query, and the plan is cached,
922 just as described above for commands that do not return rows.
923 This works for <command>SELECT</>,
924 <command>INSERT</>/<command>UPDATE</>/<command>DELETE</> with
925 <literal>RETURNING</>, and utility commands that return row-set
926 results (such as <command>EXPLAIN</>).
927 Except for the <literal>INTO</> clause, the SQL command is the same
928 as it would be written outside <application>PL/pgSQL</application>.
933 Note that this interpretation of <command>SELECT</> with <literal>INTO</>
934 is quite different from <productname>PostgreSQL</>'s regular
935 <command>SELECT INTO</command> command, wherein the <literal>INTO</>
936 target is a newly created table. If you want to create a table from a
937 <command>SELECT</> result inside a
938 <application>PL/pgSQL</application> function, use the syntax
939 <command>CREATE TABLE ... AS SELECT</command>.
944 If a row or a variable list is used as target, the query's result columns
945 must exactly match the structure of the target as to number and data
946 types, or a run-time error
947 occurs. When a record variable is the target, it automatically
948 configures itself to the row type of the query result columns.
952 The <literal>INTO</> clause can appear almost anywhere in the SQL
953 command. Customarily it is written either just before or just after
954 the list of <replaceable>select_expressions</replaceable> in a
955 <command>SELECT</> command, or at the end of the command for other
956 command types. It is recommended that you follow this convention
957 in case the <application>PL/pgSQL</application> parser becomes
958 stricter in future versions.
962 If <literal>STRICT</literal> is not specified in the <literal>INTO</>
963 clause, then <replaceable>target</replaceable> will be set to the first
964 row returned by the query, or to nulls if the query returned no rows.
965 (Note that <quote>the first row</> is not
966 well-defined unless you've used <literal>ORDER BY</>.) Any result rows
967 after the first row are discarded.
968 You can check the special <literal>FOUND</literal> variable (see
969 <xref linkend="plpgsql-statements-diagnostics">) to
970 determine whether a row was returned:
973 SELECT * INTO myrec FROM emp WHERE empname = myname;
975 RAISE EXCEPTION 'employee % not found', myname;
979 If the <literal>STRICT</literal> option is specified, the query must
980 return exactly one row or a run-time error will be reported, either
981 <literal>NO_DATA_FOUND</> (no rows) or <literal>TOO_MANY_ROWS</>
982 (more than one row). You can use an exception block if you wish
983 to catch the error, for example:
987 SELECT * INTO STRICT myrec FROM emp WHERE empname = myname;
989 WHEN NO_DATA_FOUND THEN
990 RAISE EXCEPTION 'employee % not found', myname;
991 WHEN TOO_MANY_ROWS THEN
992 RAISE EXCEPTION 'employee % not unique', myname;
995 Successful execution of a command with <literal>STRICT</>
996 always sets <literal>FOUND</literal> to true.
1000 For <command>INSERT</>/<command>UPDATE</>/<command>DELETE</> with
1001 <literal>RETURNING</>, <application>PL/pgSQL</application> reports
1002 an error for more than one returned row, even when
1003 <literal>STRICT</literal> is not specified. This is because there
1004 is no option such as <literal>ORDER BY</> with which to determine
1005 which affected row should be returned.
1010 The <literal>STRICT</> option matches the behavior of
1011 Oracle PL/SQL's <command>SELECT INTO</command> and related statements.
1016 To handle cases where you need to process multiple result rows
1017 from a SQL query, see <xref linkend="plpgsql-records-iterating">.
1022 <sect2 id="plpgsql-statements-executing-dyn">
1023 <title>Executing Dynamic Commands</title>
1026 Oftentimes you will want to generate dynamic commands inside your
1027 <application>PL/pgSQL</application> functions, that is, commands
1028 that will involve different tables or different data types each
1029 time they are executed. <application>PL/pgSQL</application>'s
1030 normal attempts to cache plans for commands (as discussed in
1031 <xref linkend="plpgsql-plan-caching">) will not work in such
1032 scenarios. To handle this sort of problem, the
1033 <command>EXECUTE</command> statement is provided:
1036 EXECUTE <replaceable class="command">command-string</replaceable> <optional> INTO <optional>STRICT</optional> <replaceable>target</replaceable> </optional> <optional> USING <replaceable>expression</replaceable> <optional>, ...</optional> </optional>;
1039 where <replaceable>command-string</replaceable> is an expression
1040 yielding a string (of type <type>text</type>) containing the
1041 command to be executed. The optional <replaceable>target</replaceable>
1042 is a record variable, a row variable, or a comma-separated list of
1043 simple variables and record/row fields, into which the results of
1044 the command will be stored. The optional <literal>USING</> expressions
1045 supply values to be inserted into the command.
1049 No substitution of <application>PL/pgSQL</> variables is done on the
1050 computed command string. Any required variable values must be inserted
1051 in the command string as it is constructed; or you can use parameters
1056 Also, there is no plan caching for commands executed via
1057 <command>EXECUTE</command>. Instead, the
1058 command is prepared each time the statement is run. Thus the command
1059 string can be dynamically created within the function to perform
1060 actions on different tables and columns.
1064 The <literal>INTO</literal> clause specifies where the results of
1065 a SQL command returning rows should be assigned. If a row
1066 or variable list is provided, it must exactly match the structure
1067 of the query's results (when a
1068 record variable is used, it will configure itself to match the
1069 result structure automatically). If multiple rows are returned,
1070 only the first will be assigned to the <literal>INTO</literal>
1071 variable. If no rows are returned, NULL is assigned to the
1072 <literal>INTO</literal> variable(s). If no <literal>INTO</literal>
1073 clause is specified, the query results are discarded.
1077 If the <literal>STRICT</> option is given, an error is reported
1078 unless the query produces exactly one row.
1082 The command string can use parameter values, which are referenced
1083 in the command as <literal>$1</>, <literal>$2</>, etc.
1084 These symbols refer to values supplied in the <literal>USING</>
1085 clause. This method is often preferable to inserting data values
1086 into the command string as text: it avoids run-time overhead of
1087 converting the values to text and back, and it is much less prone
1088 to SQL-injection attacks since there is no need for quoting or escaping.
1091 EXECUTE 'SELECT count(*) FROM mytable WHERE inserted_by = $1 AND inserted <= $2'
1093 USING checked_user, checked_date;
1096 Note that parameter symbols can only be used for data values
1097 — if you want to use dynamically determined table or column
1098 names, you must insert them into the command string textually.
1099 For example, if the preceding query needed to be done against a
1100 dynamically selected table, you could do this:
1102 EXECUTE 'SELECT count(*) FROM '
1103 || tabname::regclass
1104 || ' WHERE inserted_by = $1 AND inserted <= $2'
1106 USING checked_user, checked_date;
1111 An <command>EXECUTE</> with a simple constant command string and some
1112 <literal>USING</> parameters, as in the first example above, is
1113 functionally equivalent to just writing the command directly in
1114 <application>PL/pgSQL</application> and allowing replacement of
1115 <application>PL/pgSQL</application> variables to happen automatically.
1116 The important difference is that <command>EXECUTE</> will re-plan
1117 the command on each execution, generating a plan that is specific
1118 to the current parameter values; whereas
1119 <application>PL/pgSQL</application> normally creates a generic plan
1120 and caches it for re-use. In situations where the best plan depends
1121 strongly on the parameter values, <command>EXECUTE</> can be
1122 significantly faster; while when the plan is not sensitive to parameter
1123 values, re-planning will be a waste.
1127 <command>SELECT INTO</command> is not currently supported within
1128 <command>EXECUTE</command>; instead, execute a plain <command>SELECT</>
1129 command and specify <literal>INTO</> as part of the <command>EXECUTE</>
1135 The <application>PL/pgSQL</application>
1136 <command>EXECUTE</command> statement is not related to the
1137 <xref linkend="sql-execute" endterm="sql-execute-title"> SQL
1138 statement supported by the
1139 <productname>PostgreSQL</productname> server. The server's
1140 <command>EXECUTE</command> statement cannot be used directly within
1141 <application>PL/pgSQL</> functions (and is not needed).
1145 <example id="plpgsql-quote-literal-example">
1146 <title>Quoting values in dynamic queries</title>
1149 <primary>quote_ident</primary>
1150 <secondary>use in PL/PgSQL</secondary>
1154 <primary>quote_literal</primary>
1155 <secondary>use in PL/PgSQL</secondary>
1159 <primary>quote_nullable</primary>
1160 <secondary>use in PL/PgSQL</secondary>
1164 When working with dynamic commands you will often have to handle escaping
1165 of single quotes. The recommended method for quoting fixed text in your
1166 function body is dollar quoting. (If you have legacy code that does
1167 not use dollar quoting, please refer to the
1168 overview in <xref linkend="plpgsql-quote-tips">, which can save you
1169 some effort when translating said code to a more reasonable scheme.)
1173 Dynamic values that are to be inserted into the constructed
1174 query require careful handling since they might themselves contain
1176 An example (this assumes that you are using dollar quoting for the
1177 function as a whole, so the quote marks need not be doubled):
1179 EXECUTE 'UPDATE tbl SET '
1180 || quote_ident(colname)
1182 || quote_literal(newvalue)
1184 || quote_literal(keyvalue);
1189 This example demonstrates the use of the
1190 <function>quote_ident</function> and
1191 <function>quote_literal</function> functions (see <xref
1192 linkend="functions-string">). For safety, expressions containing column
1193 or table identifiers should be passed through
1194 <function>quote_ident</function> before insertion in a dynamic query.
1195 Expressions containing values that should be literal strings in the
1196 constructed command should be passed through <function>quote_literal</>.
1197 These functions take the appropriate steps to return the input text
1198 enclosed in double or single quotes respectively, with any embedded
1199 special characters properly escaped.
1203 Because <function>quote_literal</function> is labelled
1204 <literal>STRICT</literal>, it will always return null when called with a
1205 null argument. In the above example, if <literal>newvalue</> or
1206 <literal>keyvalue</> were null, the entire dynamic query string would
1207 become null, leading to an error from <command>EXECUTE</command>.
1208 You can avoid this problem by using the <function>quote_nullable</>
1209 function, which works the same as <function>quote_literal</> except that
1210 when called with a null argument it returns the string <literal>NULL</>.
1213 EXECUTE 'UPDATE tbl SET '
1214 || quote_ident(colname)
1216 || quote_nullable(newvalue)
1218 || quote_nullable(keyvalue);
1220 If you are dealing with values that might be null, you should usually
1221 use <function>quote_nullable</> in place of <function>quote_literal</>.
1225 As always, care must be taken to ensure that null values in a query do
1226 not deliver unintended results. For example the <literal>WHERE</> clause
1228 'WHERE key = ' || quote_nullable(keyvalue)
1230 will never succeed if <literal>keyvalue</> is null, because the
1231 result of using the equality operator <literal>=</> with a null operand
1232 is always null. If you wish null to work like an ordinary key value,
1233 you would need to rewrite the above as
1235 'WHERE key IS NOT DISTINCT FROM ' || quote_nullable(keyvalue)
1237 (At present, <literal>IS NOT DISTINCT FROM</> is handled much less
1238 efficiently than <literal>=</>, so don't do this unless you must.
1239 See <xref linkend="functions-comparison"> for
1240 more information on nulls and <literal>IS DISTINCT</>.)
1244 Note that dollar quoting is only useful for quoting fixed text.
1245 It would be a very bad idea to try to write this example as:
1247 EXECUTE 'UPDATE tbl SET '
1248 || quote_ident(colname)
1251 || '$$ WHERE key = '
1252 || quote_literal(keyvalue);
1254 because it would break if the contents of <literal>newvalue</>
1255 happened to contain <literal>$$</>. The same objection would
1256 apply to any other dollar-quoting delimiter you might pick.
1257 So, to safely quote text that is not known in advance, you
1258 <emphasis>must</> use <function>quote_literal</>,
1259 <function>quote_nullable</>, or <function>quote_ident</>, as appropriate.
1264 A much larger example of a dynamic command and
1265 <command>EXECUTE</command> can be seen in <xref
1266 linkend="plpgsql-porting-ex2">, which builds and executes a
1267 <command>CREATE FUNCTION</> command to define a new function.
1271 <sect2 id="plpgsql-statements-diagnostics">
1272 <title>Obtaining the Result Status</title>
1275 There are several ways to determine the effect of a command. The
1276 first method is to use the <command>GET DIAGNOSTICS</command>
1277 command, which has the form:
1280 GET DIAGNOSTICS <replaceable>variable</replaceable> = <replaceable>item</replaceable> <optional> , ... </optional>;
1283 This command allows retrieval of system status indicators. Each
1284 <replaceable>item</replaceable> is a key word identifying a state
1285 value to be assigned to the specified variable (which should be
1286 of the right data type to receive it). The currently available
1287 status items are <varname>ROW_COUNT</>, the number of rows
1288 processed by the last <acronym>SQL</acronym> command sent down to
1289 the <acronym>SQL</acronym> engine, and <varname>RESULT_OID</>,
1290 the OID of the last row inserted by the most recent
1291 <acronym>SQL</acronym> command. Note that <varname>RESULT_OID</>
1292 is only useful after an <command>INSERT</command> command into a
1293 table containing OIDs.
1299 GET DIAGNOSTICS integer_var = ROW_COUNT;
1304 The second method to determine the effects of a command is to check the
1305 special variable named <literal>FOUND</literal>, which is of
1306 type <type>boolean</type>. <literal>FOUND</literal> starts out
1307 false within each <application>PL/pgSQL</application> function call.
1308 It is set by each of the following types of statements:
1312 A <command>SELECT INTO</command> statement sets
1313 <literal>FOUND</literal> true if a row is assigned, false if no
1319 A <command>PERFORM</> statement sets <literal>FOUND</literal>
1320 true if it produces (and discards) one or more rows, false if
1326 <command>UPDATE</>, <command>INSERT</>, and <command>DELETE</>
1327 statements set <literal>FOUND</literal> true if at least one
1328 row is affected, false if no row is affected.
1333 A <command>FETCH</> statement sets <literal>FOUND</literal>
1334 true if it returns a row, false if no row is returned.
1339 A <command>MOVE</> statement sets <literal>FOUND</literal>
1340 true if it successfully repositions the cursor, false otherwise.
1346 A <command>FOR</> statement sets <literal>FOUND</literal> true
1347 if it iterates one or more times, else false. This applies to
1348 all four variants of the <command>FOR</> statement (integer
1349 <command>FOR</> loops, record-set <command>FOR</> loops,
1350 dynamic record-set <command>FOR</> loops, and cursor
1351 <command>FOR</> loops).
1352 <literal>FOUND</literal> is set this way when the
1353 <command>FOR</> loop exits; inside the execution of the loop,
1354 <literal>FOUND</literal> is not modified by the
1355 <command>FOR</> statement, although it might be changed by the
1356 execution of other statements within the loop body.
1361 <literal>FOUND</literal> is a local variable within each
1362 <application>PL/pgSQL</application> function; any changes to it
1363 affect only the current function.
1368 <sect2 id="plpgsql-statements-null">
1369 <title>Doing Nothing At All</title>
1372 Sometimes a placeholder statement that does nothing is useful.
1373 For example, it can indicate that one arm of an if/then/else
1374 chain is deliberately empty. For this purpose, use the
1375 <command>NULL</command> statement:
1383 For example, the following two fragments of code are equivalent:
1388 WHEN division_by_zero THEN
1389 NULL; -- ignore the error
1397 WHEN division_by_zero THEN -- ignore the error
1400 Which is preferable is a matter of taste.
1405 In Oracle's PL/SQL, empty statement lists are not allowed, and so
1406 <command>NULL</> statements are <emphasis>required</> for situations
1407 such as this. <application>PL/pgSQL</application> allows you to
1408 just write nothing, instead.
1415 <sect1 id="plpgsql-control-structures">
1416 <title>Control Structures</title>
1419 Control structures are probably the most useful (and
1420 important) part of <application>PL/pgSQL</>. With
1421 <application>PL/pgSQL</>'s control structures,
1422 you can manipulate <productname>PostgreSQL</> data in a very
1423 flexible and powerful way.
1426 <sect2 id="plpgsql-statements-returning">
1427 <title>Returning From a Function</title>
1430 There are two commands available that allow you to return data
1431 from a function: <command>RETURN</command> and <command>RETURN
1436 <title><command>RETURN</></title>
1439 RETURN <replaceable>expression</replaceable>;
1443 <command>RETURN</command> with an expression terminates the
1444 function and returns the value of
1445 <replaceable>expression</replaceable> to the caller. This form
1446 is to be used for <application>PL/pgSQL</> functions that do
1451 When returning a scalar type, any expression can be used. The
1452 expression's result will be automatically cast into the
1453 function's return type as described for assignments. To return a
1454 composite (row) value, you must write a record or row variable
1455 as the <replaceable>expression</replaceable>.
1459 If you declared the function with output parameters, write just
1460 <command>RETURN</command> with no expression. The current values
1461 of the output parameter variables will be returned.
1465 If you declared the function to return <type>void</type>, a
1466 <command>RETURN</command> statement can be used to exit the function
1467 early; but do not write an expression following
1468 <command>RETURN</command>.
1472 The return value of a function cannot be left undefined. If
1473 control reaches the end of the top-level block of the function
1474 without hitting a <command>RETURN</command> statement, a run-time
1475 error will occur. This restriction does not apply to functions
1476 with output parameters and functions returning <type>void</type>,
1477 however. In those cases a <command>RETURN</command> statement is
1478 automatically executed if the top-level block finishes.
1483 <title><command>RETURN NEXT</> and <command>RETURN QUERY</command></title>
1485 <primary>RETURN NEXT</primary>
1486 <secondary>in PL/PgSQL</secondary>
1489 <primary>RETURN QUERY</primary>
1490 <secondary>in PL/PgSQL</secondary>
1494 RETURN NEXT <replaceable>expression</replaceable>;
1495 RETURN QUERY <replaceable>query</replaceable>;
1496 RETURN QUERY EXECUTE <replaceable class="command">command-string</replaceable> <optional> USING <replaceable>expression</replaceable> <optional>, ...</optional> </optional>;
1500 When a <application>PL/pgSQL</> function is declared to return
1501 <literal>SETOF <replaceable>sometype</></literal>, the procedure
1502 to follow is slightly different. In that case, the individual
1503 items to return are specified by a sequence of <command>RETURN
1504 NEXT</command> or <command>RETURN QUERY</command> commands, and
1505 then a final <command>RETURN</command> command with no argument
1506 is used to indicate that the function has finished executing.
1507 <command>RETURN NEXT</command> can be used with both scalar and
1508 composite data types; with a composite result type, an entire
1509 <quote>table</quote> of results will be returned.
1510 <command>RETURN QUERY</command> appends the results of executing
1511 a query to the function's result set. <command>RETURN
1512 NEXT</command> and <command>RETURN QUERY</command> can be freely
1513 intermixed in a single set-returning function, in which case
1514 their results will be concatenated.
1518 <command>RETURN NEXT</command> and <command>RETURN
1519 QUERY</command> do not actually return from the function —
1520 they simply append zero or more rows to the function's result
1521 set. Execution then continues with the next statement in the
1522 <application>PL/pgSQL</> function. As successive
1523 <command>RETURN NEXT</command> or <command>RETURN
1524 QUERY</command> commands are executed, the result set is built
1525 up. A final <command>RETURN</command>, which should have no
1526 argument, causes control to exit the function (or you can just
1527 let control reach the end of the function).
1531 <command>RETURN QUERY</command> has a variant
1532 <command>RETURN QUERY EXECUTE</command>, which specifies the
1533 query to be executed dynamically. Parameter expressions can
1534 be inserted into the computed query string via <literal>USING</>,
1535 in just the same way as in the <command>EXECUTE</> command.
1539 If you declared the function with output parameters, write just
1540 <command>RETURN NEXT</command> with no expression. On each
1541 execution, the current values of the output parameter
1542 variable(s) will be saved for eventual return as a row of the
1543 result. Note that you must declare the function as returning
1544 <literal>SETOF record</literal> when there are multiple output
1545 parameters, or <literal>SETOF <replaceable>sometype</></literal>
1546 when there is just one output parameter of type
1547 <replaceable>sometype</>, in order to create a set-returning
1548 function with output parameters.
1552 Here is an example of a function using <command>RETURN
1556 CREATE TABLE foo (fooid INT, foosubid INT, fooname TEXT);
1557 INSERT INTO foo VALUES (1, 2, 'three');
1558 INSERT INTO foo VALUES (4, 5, 'six');
1560 CREATE OR REPLACE FUNCTION getAllFoo() RETURNS SETOF foo AS
1565 FOR r IN SELECT * FROM foo
1568 -- can do some processing here
1569 RETURN NEXT r; -- return current row of SELECT
1574 LANGUAGE 'plpgsql' ;
1576 SELECT * FROM getallfoo();
1582 The current implementation of <command>RETURN NEXT</command>
1583 and <command>RETURN QUERY</command> stores the entire result set
1584 before returning from the function, as discussed above. That
1585 means that if a <application>PL/pgSQL</> function produces a
1586 very large result set, performance might be poor: data will be
1587 written to disk to avoid memory exhaustion, but the function
1588 itself will not return until the entire result set has been
1589 generated. A future version of <application>PL/pgSQL</> might
1590 allow users to define set-returning functions
1591 that do not have this limitation. Currently, the point at
1592 which data begins being written to disk is controlled by the
1593 <xref linkend="guc-work-mem">
1594 configuration variable. Administrators who have sufficient
1595 memory to store larger result sets in memory should consider
1596 increasing this parameter.
1602 <sect2 id="plpgsql-conditionals">
1603 <title>Conditionals</title>
1606 <command>IF</> and <command>CASE</> statements let you execute
1607 alternative commands based on certain conditions.
1608 <application>PL/pgSQL</> has three forms of <command>IF</>:
1611 <para><literal>IF ... THEN</></>
1614 <para><literal>IF ... THEN ... ELSE</></>
1617 <para><literal>IF ... THEN ... ELSIF ... THEN ... ELSE</></>
1621 and two forms of <command>CASE</>:
1624 <para><literal>CASE ... WHEN ... THEN ... ELSE ... END CASE</></>
1627 <para><literal>CASE WHEN ... THEN ... ELSE ... END CASE</></>
1633 <title><literal>IF-THEN</></title>
1636 IF <replaceable>boolean-expression</replaceable> THEN
1637 <replaceable>statements</replaceable>
1642 <literal>IF-THEN</literal> statements are the simplest form of
1643 <literal>IF</literal>. The statements between
1644 <literal>THEN</literal> and <literal>END IF</literal> will be
1645 executed if the condition is true. Otherwise, they are
1652 IF v_user_id <> 0 THEN
1653 UPDATE users SET email = v_email WHERE user_id = v_user_id;
1660 <title><literal>IF-THEN-ELSE</></title>
1663 IF <replaceable>boolean-expression</replaceable> THEN
1664 <replaceable>statements</replaceable>
1666 <replaceable>statements</replaceable>
1671 <literal>IF-THEN-ELSE</literal> statements add to
1672 <literal>IF-THEN</literal> by letting you specify an
1673 alternative set of statements that should be executed if the
1674 condition is not true. (Note this includes the case where the
1675 condition evaluates to NULL.)
1681 IF parentid IS NULL OR parentid = ''
1685 RETURN hp_true_filename(parentid) || '/' || fullname;
1690 IF v_count > 0 THEN
1691 INSERT INTO users_count (count) VALUES (v_count);
1701 <title><literal>IF-THEN-ELSIF</></title>
1704 IF <replaceable>boolean-expression</replaceable> THEN
1705 <replaceable>statements</replaceable>
1706 <optional> ELSIF <replaceable>boolean-expression</replaceable> THEN
1707 <replaceable>statements</replaceable>
1708 <optional> ELSIF <replaceable>boolean-expression</replaceable> THEN
1709 <replaceable>statements</replaceable>
1714 <replaceable>statements</replaceable> </optional>
1719 Sometimes there are more than just two alternatives.
1720 <literal>IF-THEN-ELSIF</> provides a convenient
1721 method of checking several alternatives in turn.
1722 The <literal>IF</> conditions are tested successively
1723 until the first one that is true is found. Then the
1724 associated statement(s) are executed, after which control
1725 passes to the next statement after <literal>END IF</>.
1726 (Any subsequent <literal>IF</> conditions are <emphasis>not</>
1727 tested.) If none of the <literal>IF</> conditions is true,
1728 then the <literal>ELSE</> block (if any) is executed.
1737 ELSIF number > 0 THEN
1738 result := 'positive';
1739 ELSIF number < 0 THEN
1740 result := 'negative';
1742 -- hmm, the only other possibility is that number is null
1749 The key word <literal>ELSIF</> can also be spelled
1754 An alternative way of accomplishing the same task is to nest
1755 <literal>IF-THEN-ELSE</literal> statements, as in the
1759 IF demo_row.sex = 'm' THEN
1760 pretty_sex := 'man';
1762 IF demo_row.sex = 'f' THEN
1763 pretty_sex := 'woman';
1770 However, this method requires writing a matching <literal>END IF</>
1771 for each <literal>IF</>, so it is much more cumbersome than
1772 using <literal>ELSIF</> when there are many alternatives.
1777 <title>Simple <literal>CASE</></title>
1780 CASE <replaceable>search-expression</replaceable>
1781 WHEN <replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> <optional> ... </optional></optional> THEN
1782 <replaceable>statements</replaceable>
1783 <optional> WHEN <replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> <optional> ... </optional></optional> THEN
1784 <replaceable>statements</replaceable>
1787 <replaceable>statements</replaceable> </optional>
1792 The simple form of <command>CASE</> provides conditional execution
1793 based on equality of operands. The <replaceable>search-expression</>
1794 is evaluated (once) and successively compared to each
1795 <replaceable>expression</> in the <literal>WHEN</> clauses.
1796 If a match is found, then the corresponding
1797 <replaceable>statements</replaceable> are executed, and then control
1798 passes to the next statement after <literal>END CASE</>. (Subsequent
1799 <literal>WHEN</> expressions are not evaluated.) If no match is
1800 found, the <literal>ELSE</> <replaceable>statements</replaceable> are
1801 executed; but if <literal>ELSE</> is not present, then a
1802 <literal>CASE_NOT_FOUND</literal> exception is raised.
1806 Here is a simple example:
1811 msg := 'one or two';
1813 msg := 'other value than one or two';
1820 <title>Searched <literal>CASE</></title>
1824 WHEN <replaceable>boolean-expression</replaceable> THEN
1825 <replaceable>statements</replaceable>
1826 <optional> WHEN <replaceable>boolean-expression</replaceable> THEN
1827 <replaceable>statements</replaceable>
1830 <replaceable>statements</replaceable> </optional>
1835 The searched form of <command>CASE</> provides conditional execution
1836 based on truth of boolean expressions. Each <literal>WHEN</> clause's
1837 <replaceable>boolean-expression</replaceable> is evaluated in turn,
1838 until one is found that yields <literal>true</>. Then the
1839 corresponding <replaceable>statements</replaceable> are executed, and
1840 then control passes to the next statement after <literal>END CASE</>.
1841 (Subsequent <literal>WHEN</> expressions are not evaluated.)
1842 If no true result is found, the <literal>ELSE</>
1843 <replaceable>statements</replaceable> are executed;
1844 but if <literal>ELSE</> is not present, then a
1845 <literal>CASE_NOT_FOUND</literal> exception is raised.
1853 WHEN x BETWEEN 0 AND 10 THEN
1854 msg := 'value is between zero and ten';
1855 WHEN x BETWEEN 11 AND 20 THEN
1856 msg := 'value is between eleven and twenty';
1862 This form of <command>CASE</> is entirely equivalent to
1863 <literal>IF-THEN-ELSIF</>, except for the rule that reaching
1864 an omitted <literal>ELSE</> clause results in an error rather
1871 <sect2 id="plpgsql-control-structures-loops">
1872 <title>Simple Loops</title>
1874 <indexterm zone="plpgsql-control-structures-loops">
1875 <primary>loop</primary>
1876 <secondary>in PL/pgSQL</secondary>
1880 With the <literal>LOOP</>, <literal>EXIT</>,
1881 <literal>CONTINUE</>, <literal>WHILE</>, and <literal>FOR</>
1882 statements, you can arrange for your <application>PL/pgSQL</>
1883 function to repeat a series of commands.
1887 <title><literal>LOOP</></title>
1890 <optional> <<<replaceable>label</replaceable>>> </optional>
1892 <replaceable>statements</replaceable>
1893 END LOOP <optional> <replaceable>label</replaceable> </optional>;
1897 <literal>LOOP</> defines an unconditional loop that is repeated
1898 indefinitely until terminated by an <literal>EXIT</> or
1899 <command>RETURN</command> statement. The optional
1900 <replaceable>label</replaceable> can be used by <literal>EXIT</>
1901 and <literal>CONTINUE</literal> statements in nested loops to
1902 specify which loop the statement should be applied to.
1907 <title><literal>EXIT</></title>
1910 <primary>EXIT</primary>
1911 <secondary>in PL/pgSQL</secondary>
1915 EXIT <optional> <replaceable>label</replaceable> </optional> <optional> WHEN <replaceable>boolean-expression</replaceable> </optional>;
1919 If no <replaceable>label</replaceable> is given, the innermost
1920 loop is terminated and the statement following <literal>END
1921 LOOP</> is executed next. If <replaceable>label</replaceable>
1922 is given, it must be the label of the current or some outer
1923 level of nested loop or block. Then the named loop or block is
1924 terminated and control continues with the statement after the
1925 loop's/block's corresponding <literal>END</>.
1929 If <literal>WHEN</> is specified, the loop exit occurs only if
1930 <replaceable>boolean-expression</> is true. Otherwise, control passes
1931 to the statement after <literal>EXIT</>.
1935 <literal>EXIT</> can be used with all types of loops; it is
1936 not limited to use with unconditional loops. When used with a
1937 <literal>BEGIN</literal> block, <literal>EXIT</literal> passes
1938 control to the next statement after the end of the block.
1945 -- some computations
1946 IF count > 0 THEN
1952 -- some computations
1953 EXIT WHEN count > 0; -- same result as previous example
1957 -- some computations
1958 IF stocks > 100000 THEN
1959 EXIT; -- causes exit from the BEGIN block
1967 <title><literal>CONTINUE</></title>
1970 <primary>CONTINUE</primary>
1971 <secondary>in PL/pgSQL</secondary>
1975 CONTINUE <optional> <replaceable>label</replaceable> </optional> <optional> WHEN <replaceable>boolean-expression</replaceable> </optional>;
1979 If no <replaceable>label</> is given, the next iteration of
1980 the innermost loop is begun. That is, all statements remaining
1981 in the loop body are skipped, and control returns
1982 to the loop control expression (if any) to determine whether
1983 another loop iteration is needed.
1984 If <replaceable>label</> is present, it
1985 specifies the label of the loop whose execution will be
1990 If <literal>WHEN</> is specified, the next iteration of the
1991 loop is begun only if <replaceable>boolean-expression</> is
1992 true. Otherwise, control passes to the statement after
1993 <literal>CONTINUE</>.
1997 <literal>CONTINUE</> can be used with all types of loops; it
1998 is not limited to use with unconditional loops.
2005 -- some computations
2006 EXIT WHEN count > 100;
2007 CONTINUE WHEN count < 50;
2008 -- some computations for count IN [50 .. 100]
2016 <title><literal>WHILE</></title>
2019 <primary>WHILE</primary>
2020 <secondary>in PL/pgSQL</secondary>
2024 <optional> <<<replaceable>label</replaceable>>> </optional>
2025 WHILE <replaceable>boolean-expression</replaceable> LOOP
2026 <replaceable>statements</replaceable>
2027 END LOOP <optional> <replaceable>label</replaceable> </optional>;
2031 The <literal>WHILE</> statement repeats a
2032 sequence of statements so long as the
2033 <replaceable>boolean-expression</replaceable>
2034 evaluates to true. The expression is checked just before
2035 each entry to the loop body.
2041 WHILE amount_owed > 0 AND gift_certificate_balance > 0 LOOP
2042 -- some computations here
2046 -- some computations here
2052 <sect3 id="plpgsql-integer-for">
2053 <title><literal>FOR</> (integer variant)</title>
2056 <optional> <<<replaceable>label</replaceable>>> </optional>
2057 FOR <replaceable>name</replaceable> IN <optional> REVERSE </optional> <replaceable>expression</replaceable> .. <replaceable>expression</replaceable> <optional> BY <replaceable>expression</replaceable> </optional> LOOP
2058 <replaceable>statements</replaceable>
2059 END LOOP <optional> <replaceable>label</replaceable> </optional>;
2063 This form of <literal>FOR</> creates a loop that iterates over a range
2064 of integer values. The variable
2065 <replaceable>name</replaceable> is automatically defined as type
2066 <type>integer</> and exists only inside the loop (any existing
2067 definition of the variable name is ignored within the loop).
2068 The two expressions giving
2069 the lower and upper bound of the range are evaluated once when entering
2070 the loop. If the <literal>BY</> clause isn't specified the iteration
2071 step is 1, otherwise it's the value specified in the <literal>BY</>
2072 clause, which again is evaluated once on loop entry.
2073 If <literal>REVERSE</> is specified then the step value is
2074 subtracted, rather than added, after each iteration.
2078 Some examples of integer <literal>FOR</> loops:
2081 -- i will take on the values 1,2,3,4,5,6,7,8,9,10 within the loop
2084 FOR i IN REVERSE 10..1 LOOP
2085 -- i will take on the values 10,9,8,7,6,5,4,3,2,1 within the loop
2088 FOR i IN REVERSE 10..1 BY 2 LOOP
2089 -- i will take on the values 10,8,6,4,2 within the loop
2095 If the lower bound is greater than the upper bound (or less than,
2096 in the <literal>REVERSE</> case), the loop body is not
2097 executed at all. No error is raised.
2101 If a <replaceable>label</replaceable> is attached to the
2102 <literal>FOR</> loop then the integer loop variable can be
2103 referenced with a qualified name, using that
2104 <replaceable>label</replaceable>.
2109 <sect2 id="plpgsql-records-iterating">
2110 <title>Looping Through Query Results</title>
2113 Using a different type of <literal>FOR</> loop, you can iterate through
2114 the results of a query and manipulate that data
2115 accordingly. The syntax is:
2117 <optional> <<<replaceable>label</replaceable>>> </optional>
2118 FOR <replaceable>target</replaceable> IN <replaceable>query</replaceable> LOOP
2119 <replaceable>statements</replaceable>
2120 END LOOP <optional> <replaceable>label</replaceable> </optional>;
2122 The <replaceable>target</replaceable> is a record variable, row variable,
2123 or comma-separated list of scalar variables.
2124 The <replaceable>target</replaceable> is successively assigned each row
2125 resulting from the <replaceable>query</replaceable> and the loop body is
2126 executed for each row. Here is an example:
2128 CREATE FUNCTION cs_refresh_mviews() RETURNS integer AS $$
2132 PERFORM cs_log('Refreshing materialized views...');
2134 FOR mviews IN SELECT * FROM cs_materialized_views ORDER BY sort_key LOOP
2136 -- Now "mviews" has one record from cs_materialized_views
2138 PERFORM cs_log('Refreshing materialized view ' || quote_ident(mviews.mv_name) || ' ...');
2139 EXECUTE 'TRUNCATE TABLE ' || quote_ident(mviews.mv_name);
2140 EXECUTE 'INSERT INTO ' || quote_ident(mviews.mv_name) || ' ' || mviews.mv_query;
2143 PERFORM cs_log('Done refreshing materialized views.');
2146 $$ LANGUAGE plpgsql;
2149 If the loop is terminated by an <literal>EXIT</> statement, the last
2150 assigned row value is still accessible after the loop.
2154 The <replaceable>query</replaceable> used in this type of <literal>FOR</>
2155 statement can be any SQL command that returns rows to the caller:
2156 <command>SELECT</> is the most common case,
2157 but you can also use <command>INSERT</>, <command>UPDATE</>, or
2158 <command>DELETE</> with a <literal>RETURNING</> clause. Some utility
2159 commands such as <command>EXPLAIN</> will work too.
2163 <application>PL/pgSQL</> variables are substituted into the query text,
2164 and the query plan is cached for possible re-use, as discussed in
2165 detail in <xref linkend="plpgsql-var-subst"> and
2166 <xref linkend="plpgsql-plan-caching">.
2170 The <literal>FOR-IN-EXECUTE</> statement is another way to iterate over
2173 <optional> <<<replaceable>label</replaceable>>> </optional>
2174 FOR <replaceable>target</replaceable> IN EXECUTE <replaceable>text_expression</replaceable> <optional> USING <replaceable>expression</replaceable> <optional>, ...</optional> </optional> LOOP
2175 <replaceable>statements</replaceable>
2176 END LOOP <optional> <replaceable>label</replaceable> </optional>;
2178 This is like the previous form, except that the source query
2179 is specified as a string expression, which is evaluated and replanned
2180 on each entry to the <literal>FOR</> loop. This allows the programmer to
2181 choose the speed of a preplanned query or the flexibility of a dynamic
2182 query, just as with a plain <command>EXECUTE</command> statement.
2183 As with <command>EXECUTE</command>, parameter values can be inserted
2184 into the dynamic command via <literal>USING</>.
2188 Another way to specify the query whose results should be iterated
2189 through is to declare it as a cursor. This is described in
2190 <xref linkend="plpgsql-cursor-for-loop">.
2194 <sect2 id="plpgsql-error-trapping">
2195 <title>Trapping Errors</title>
2198 <primary>exceptions</primary>
2199 <secondary>in PL/PgSQL</secondary>
2203 By default, any error occurring in a <application>PL/pgSQL</>
2204 function aborts execution of the function, and indeed of the
2205 surrounding transaction as well. You can trap errors and recover
2206 from them by using a <command>BEGIN</> block with an
2207 <literal>EXCEPTION</> clause. The syntax is an extension of the
2208 normal syntax for a <command>BEGIN</> block:
2211 <optional> <<<replaceable>label</replaceable>>> </optional>
2213 <replaceable>declarations</replaceable> </optional>
2215 <replaceable>statements</replaceable>
2217 WHEN <replaceable>condition</replaceable> <optional> OR <replaceable>condition</replaceable> ... </optional> THEN
2218 <replaceable>handler_statements</replaceable>
2219 <optional> WHEN <replaceable>condition</replaceable> <optional> OR <replaceable>condition</replaceable> ... </optional> THEN
2220 <replaceable>handler_statements</replaceable>
2227 If no error occurs, this form of block simply executes all the
2228 <replaceable>statements</replaceable>, and then control passes
2229 to the next statement after <literal>END</>. But if an error
2230 occurs within the <replaceable>statements</replaceable>, further
2231 processing of the <replaceable>statements</replaceable> is
2232 abandoned, and control passes to the <literal>EXCEPTION</> list.
2233 The list is searched for the first <replaceable>condition</replaceable>
2234 matching the error that occurred. If a match is found, the
2235 corresponding <replaceable>handler_statements</replaceable> are
2236 executed, and then control passes to the next statement after
2237 <literal>END</>. If no match is found, the error propagates out
2238 as though the <literal>EXCEPTION</> clause were not there at all:
2239 the error can be caught by an enclosing block with
2240 <literal>EXCEPTION</>, or if there is none it aborts processing
2245 The <replaceable>condition</replaceable> names can be any of
2246 those shown in <xref linkend="errcodes-appendix">. A category
2247 name matches any error within its category. The special
2248 condition name <literal>OTHERS</> matches every error type except
2249 <literal>QUERY_CANCELED</>. (It is possible, but often unwise,
2250 to trap <literal>QUERY_CANCELED</> by name.) Condition names are
2251 not case-sensitive. Also, an error condition can be specified
2252 by <literal>SQLSTATE</> code; for example these are equivalent:
2254 WHEN division_by_zero THEN ...
2255 WHEN SQLSTATE '22012' THEN ...
2260 If a new error occurs within the selected
2261 <replaceable>handler_statements</replaceable>, it cannot be caught
2262 by this <literal>EXCEPTION</> clause, but is propagated out.
2263 A surrounding <literal>EXCEPTION</> clause could catch it.
2267 When an error is caught by an <literal>EXCEPTION</> clause,
2268 the local variables of the <application>PL/pgSQL</> function
2269 remain as they were when the error occurred, but all changes
2270 to persistent database state within the block are rolled back.
2271 As an example, consider this fragment:
2274 INSERT INTO mytab(firstname, lastname) VALUES('Tom', 'Jones');
2276 UPDATE mytab SET firstname = 'Joe' WHERE lastname = 'Jones';
2280 WHEN division_by_zero THEN
2281 RAISE NOTICE 'caught division_by_zero';
2286 When control reaches the assignment to <literal>y</>, it will
2287 fail with a <literal>division_by_zero</> error. This will be caught by
2288 the <literal>EXCEPTION</> clause. The value returned in the
2289 <command>RETURN</> statement will be the incremented value of
2290 <literal>x</>, but the effects of the <command>UPDATE</> command will
2291 have been rolled back. The <command>INSERT</> command preceding the
2292 block is not rolled back, however, so the end result is that the database
2293 contains <literal>Tom Jones</> not <literal>Joe Jones</>.
2298 A block containing an <literal>EXCEPTION</> clause is significantly
2299 more expensive to enter and exit than a block without one. Therefore,
2300 don't use <literal>EXCEPTION</> without need.
2305 Within an exception handler, the <varname>SQLSTATE</varname>
2306 variable contains the error code that corresponds to the
2307 exception that was raised (refer to <xref
2308 linkend="errcodes-table"> for a list of possible error
2309 codes). The <varname>SQLERRM</varname> variable contains the
2310 error message associated with the exception. These variables are
2311 undefined outside exception handlers.
2314 <example id="plpgsql-upsert-example">
2315 <title>Exceptions with <command>UPDATE</>/<command>INSERT</></title>
2318 This example uses exception handling to perform either
2319 <command>UPDATE</> or <command>INSERT</>, as appropriate:
2322 CREATE TABLE db (a INT PRIMARY KEY, b TEXT);
2324 CREATE FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS
2328 -- first try to update the key
2329 UPDATE db SET b = data WHERE a = key;
2333 -- not there, so try to insert the key
2334 -- if someone else inserts the same key concurrently,
2335 -- we could get a unique-key failure
2337 INSERT INTO db(a,b) VALUES (key, data);
2339 EXCEPTION WHEN unique_violation THEN
2340 -- do nothing, and loop to try the UPDATE again
2347 SELECT merge_db(1, 'david');
2348 SELECT merge_db(1, 'dennis');
2356 <sect1 id="plpgsql-cursors">
2357 <title>Cursors</title>
2359 <indexterm zone="plpgsql-cursors">
2360 <primary>cursor</primary>
2361 <secondary>in PL/pgSQL</secondary>
2365 Rather than executing a whole query at once, it is possible to set
2366 up a <firstterm>cursor</> that encapsulates the query, and then read
2367 the query result a few rows at a time. One reason for doing this is
2368 to avoid memory overrun when the result contains a large number of
2369 rows. (However, <application>PL/pgSQL</> users do not normally need
2370 to worry about that, since <literal>FOR</> loops automatically use a cursor
2371 internally to avoid memory problems.) A more interesting usage is to
2372 return a reference to a cursor that a function has created, allowing the
2373 caller to read the rows. This provides an efficient way to return
2374 large row sets from functions.
2377 <sect2 id="plpgsql-cursor-declarations">
2378 <title>Declaring Cursor Variables</title>
2381 All access to cursors in <application>PL/pgSQL</> goes through
2382 cursor variables, which are always of the special data type
2383 <type>refcursor</>. One way to create a cursor variable
2384 is just to declare it as a variable of type <type>refcursor</>.
2385 Another way is to use the cursor declaration syntax,
2386 which in general is:
2388 <replaceable>name</replaceable> <optional> <optional> NO </optional> SCROLL </optional> CURSOR <optional> ( <replaceable>arguments</replaceable> ) </optional> FOR <replaceable>query</replaceable>;
2390 (<literal>FOR</> can be replaced by <literal>IS</> for
2391 <productname>Oracle</productname> compatibility.)
2392 If <literal>SCROLL</> is specified, the cursor will be capable of
2393 scrolling backward; if <literal>NO SCROLL</> is specified, backward
2394 fetches will be rejected; if neither specification appears, it is
2395 query-dependent whether backward fetches will be allowed.
2396 <replaceable>arguments</replaceable>, if specified, is a
2397 comma-separated list of pairs <literal><replaceable>name</replaceable>
2398 <replaceable>datatype</replaceable></literal> that define names to be
2399 replaced by parameter values in the given query. The actual
2400 values to substitute for these names will be specified later,
2401 when the cursor is opened.
2408 curs2 CURSOR FOR SELECT * FROM tenk1;
2409 curs3 CURSOR (key integer) IS SELECT * FROM tenk1 WHERE unique1 = key;
2411 All three of these variables have the data type <type>refcursor</>,
2412 but the first can be used with any query, while the second has
2413 a fully specified query already <firstterm>bound</> to it, and the last
2414 has a parameterized query bound to it. (<literal>key</> will be
2415 replaced by an integer parameter value when the cursor is opened.)
2416 The variable <literal>curs1</>
2417 is said to be <firstterm>unbound</> since it is not bound to
2418 any particular query.
2422 <sect2 id="plpgsql-cursor-opening">
2423 <title>Opening Cursors</title>
2426 Before a cursor can be used to retrieve rows, it must be
2427 <firstterm>opened</>. (This is the equivalent action to the SQL
2428 command <command>DECLARE CURSOR</>.) <application>PL/pgSQL</> has
2429 three forms of the <command>OPEN</> statement, two of which use unbound
2430 cursor variables while the third uses a bound cursor variable.
2435 Bound cursors can also be used without explicitly opening them,
2436 via the <command>FOR</> statement described in
2437 <xref linkend="plpgsql-cursor-for-loop">.
2442 <title><command>OPEN FOR</command> <replaceable>query</replaceable></title>
2445 OPEN <replaceable>unbound_cursor</replaceable> <optional> <optional> NO </optional> SCROLL </optional> FOR <replaceable>query</replaceable>;
2449 The cursor variable is opened and given the specified query to
2450 execute. The cursor cannot be open already, and it must have been
2451 declared as an unbound cursor (that is, as a simple
2452 <type>refcursor</> variable). The query must be a
2453 <command>SELECT</command>, or something else that returns rows
2454 (such as <command>EXPLAIN</>). The query
2455 is treated in the same way as other SQL commands in
2456 <application>PL/pgSQL</>: <application>PL/pgSQL</>
2457 variable names are substituted, and the query plan is cached for
2458 possible reuse. When a <application>PL/pgSQL</>
2459 variable is substituted into the cursor query, the value that is
2460 substituted is the one it has at the time of the <command>OPEN</>;
2461 subsequent changes to the variable will not affect the cursor's
2463 The <literal>SCROLL</> and <literal>NO SCROLL</>
2464 options have the same meanings as for a bound cursor.
2470 OPEN curs1 FOR SELECT * FROM foo WHERE key = mykey;
2476 <title><command>OPEN FOR EXECUTE</command></title>
2479 OPEN <replaceable>unbound_cursor</replaceable> <optional> <optional> NO </optional> SCROLL </optional> FOR EXECUTE <replaceable class="command">query_string</replaceable>;
2483 The cursor variable is opened and given the specified query to
2484 execute. The cursor cannot be open already, and it must have been
2485 declared as an unbound cursor (that is, as a simple
2486 <type>refcursor</> variable). The query is specified as a string
2487 expression, in the same way as in the <command>EXECUTE</command>
2488 command. As usual, this gives flexibility so the query plan can vary
2489 from one run to the next (see <xref linkend="plpgsql-plan-caching">),
2490 and it also means that variable substitution is not done on the
2492 The <literal>SCROLL</> and
2493 <literal>NO SCROLL</> options have the same meanings as for a bound
2500 OPEN curs1 FOR EXECUTE 'SELECT * FROM ' || quote_ident($1);
2506 <title>Opening a Bound Cursor</title>
2509 OPEN <replaceable>bound_cursor</replaceable> <optional> ( <replaceable>argument_values</replaceable> ) </optional>;
2513 This form of <command>OPEN</command> is used to open a cursor
2514 variable whose query was bound to it when it was declared. The
2515 cursor cannot be open already. A list of actual argument value
2516 expressions must appear if and only if the cursor was declared to
2517 take arguments. These values will be substituted in the query.
2518 The query plan for a bound cursor is always considered cacheable;
2519 there is no equivalent of <command>EXECUTE</command> in this case.
2520 Notice that <literal>SCROLL</> and
2521 <literal>NO SCROLL</> cannot be specified, as the cursor's scrolling
2522 behavior was already determined.
2526 Note that because variable substitution is done on the bound
2527 cursor's query, there are two ways to pass values into the cursor:
2528 either with an explicit argument to <command>OPEN</>, or
2529 implicitly by referencing a <application>PL/pgSQL</> variable
2530 in the query. However, only variables declared before the bound
2531 cursor was declared will be substituted into it. In either case
2532 the value to be passed is determined at the time of the
2546 <sect2 id="plpgsql-cursor-using">
2547 <title>Using Cursors</title>
2550 Once a cursor has been opened, it can be manipulated with the
2551 statements described here.
2555 These manipulations need not occur in the same function that
2556 opened the cursor to begin with. You can return a <type>refcursor</>
2557 value out of a function and let the caller operate on the cursor.
2558 (Internally, a <type>refcursor</> value is simply the string name
2559 of a so-called portal containing the active query for the cursor. This name
2560 can be passed around, assigned to other <type>refcursor</> variables,
2561 and so on, without disturbing the portal.)
2565 All portals are implicitly closed at transaction end. Therefore
2566 a <type>refcursor</> value is usable to reference an open cursor
2567 only until the end of the transaction.
2571 <title><literal>FETCH</></title>
2574 FETCH <optional> <replaceable>direction</replaceable> { FROM | IN } </optional> <replaceable>cursor</replaceable> INTO <replaceable>target</replaceable>;
2578 <command>FETCH</command> retrieves the next row from the
2579 cursor into a target, which might be a row variable, a record
2580 variable, or a comma-separated list of simple variables, just like
2581 <command>SELECT INTO</command>. If there is no next row, the
2582 target is set to NULL(s). As with <command>SELECT
2583 INTO</command>, the special variable <literal>FOUND</literal> can
2584 be checked to see whether a row was obtained or not.
2588 The <replaceable>direction</replaceable> clause can be any of the
2589 variants allowed in the SQL <xref linkend="sql-fetch"
2590 endterm="sql-fetch-title"> command except the ones that can fetch
2591 more than one row; namely, it can be
2596 <literal>ABSOLUTE</> <replaceable>count</replaceable>,
2597 <literal>RELATIVE</> <replaceable>count</replaceable>,
2598 <literal>FORWARD</>, or
2599 <literal>BACKWARD</>.
2600 Omitting <replaceable>direction</replaceable> is the same
2601 as specifying <literal>NEXT</>.
2602 <replaceable>direction</replaceable> values that require moving
2603 backward are likely to fail unless the cursor was declared or opened
2604 with the <literal>SCROLL</> option.
2608 <replaceable>cursor</replaceable> must be the name of a <type>refcursor</>
2609 variable that references an open cursor portal.
2615 FETCH curs1 INTO rowvar;
2616 FETCH curs2 INTO foo, bar, baz;
2617 FETCH LAST FROM curs3 INTO x, y;
2618 FETCH RELATIVE -2 FROM curs4 INTO x;
2624 <title><literal>MOVE</></title>
2627 MOVE <optional> <replaceable>direction</replaceable> { FROM | IN } </optional> <replaceable>cursor</replaceable>;
2631 <command>MOVE</command> repositions a cursor without retrieving
2632 any data. <command>MOVE</command> works exactly like the
2633 <command>FETCH</command> command, except it only repositions the
2634 cursor and does not return the row moved to. As with <command>SELECT
2635 INTO</command>, the special variable <literal>FOUND</literal> can
2636 be checked to see whether there was a next row to move to.
2640 The options for the <replaceable>direction</replaceable> clause are
2641 the same as for <command>FETCH</>, namely
2646 <literal>ABSOLUTE</> <replaceable>count</replaceable>,
2647 <literal>RELATIVE</> <replaceable>count</replaceable>,
2648 <literal>FORWARD</>, or
2649 <literal>BACKWARD</>.
2650 Omitting <replaceable>direction</replaceable> is the same
2651 as specifying <literal>NEXT</>.
2652 <replaceable>direction</replaceable> values that require moving
2653 backward are likely to fail unless the cursor was declared or opened
2654 with the <literal>SCROLL</> option.
2661 MOVE LAST FROM curs3;
2662 MOVE RELATIVE -2 FROM curs4;
2668 <title><literal>UPDATE/DELETE WHERE CURRENT OF</></title>
2671 UPDATE <replaceable>table</replaceable> SET ... WHERE CURRENT OF <replaceable>cursor</replaceable>;
2672 DELETE FROM <replaceable>table</replaceable> WHERE CURRENT OF <replaceable>cursor</replaceable>;
2676 When a cursor is positioned on a table row, that row can be updated
2677 or deleted using the cursor to identify the row. There are
2678 restrictions on what the cursor's query can be (in particular,
2679 no grouping) and it's best to use <literal>FOR UPDATE</> in the
2680 cursor. For additional information see the
2681 <xref linkend="sql-declare" endterm="sql-declare-title">
2688 UPDATE foo SET dataval = myval WHERE CURRENT OF curs1;
2694 <title><literal>CLOSE</></title>
2697 CLOSE <replaceable>cursor</replaceable>;
2701 <command>CLOSE</command> closes the portal underlying an open
2702 cursor. This can be used to release resources earlier than end of
2703 transaction, or to free up the cursor variable to be opened again.
2715 <title>Returning Cursors</title>
2718 <application>PL/pgSQL</> functions can return cursors to the
2719 caller. This is useful to return multiple rows or columns,
2720 especially with very large result sets. To do this, the function
2721 opens the cursor and returns the cursor name to the caller (or simply
2722 opens the cursor using a portal name specified by or otherwise known
2723 to the caller). The caller can then fetch rows from the cursor. The
2724 cursor can be closed by the caller, or it will be closed automatically
2725 when the transaction closes.
2729 The portal name used for a cursor can be specified by the
2730 programmer or automatically generated. To specify a portal name,
2731 simply assign a string to the <type>refcursor</> variable before
2732 opening it. The string value of the <type>refcursor</> variable
2733 will be used by <command>OPEN</> as the name of the underlying portal.
2734 However, if the <type>refcursor</> variable is null,
2735 <command>OPEN</> automatically generates a name that does not
2736 conflict with any existing portal, and assigns it to the
2737 <type>refcursor</> variable.
2742 A bound cursor variable is initialized to the string value
2743 representing its name, so that the portal name is the same as
2744 the cursor variable name, unless the programmer overrides it
2745 by assignment before opening the cursor. But an unbound cursor
2746 variable defaults to the null value initially, so it will receive
2747 an automatically-generated unique name, unless overridden.
2752 The following example shows one way a cursor name can be supplied by
2756 CREATE TABLE test (col text);
2757 INSERT INTO test VALUES ('123');
2759 CREATE FUNCTION reffunc(refcursor) RETURNS refcursor AS '
2761 OPEN $1 FOR SELECT col FROM test;
2767 SELECT reffunc('funccursor');
2768 FETCH ALL IN funccursor;
2774 The following example uses automatic cursor name generation:
2777 CREATE FUNCTION reffunc2() RETURNS refcursor AS '
2781 OPEN ref FOR SELECT col FROM test;
2790 --------------------
2791 <unnamed cursor 1>
2794 FETCH ALL IN "<unnamed cursor 1>";
2800 The following example shows one way to return multiple cursors
2801 from a single function:
2804 CREATE FUNCTION myfunc(refcursor, refcursor) RETURNS SETOF refcursor AS $$
2806 OPEN $1 FOR SELECT * FROM table_1;
2808 OPEN $2 FOR SELECT * FROM table_2;
2811 $$ LANGUAGE plpgsql;
2813 -- need to be in a transaction to use cursors.
2816 SELECT * FROM myfunc('a', 'b');
2826 <sect2 id="plpgsql-cursor-for-loop">
2827 <title>Looping Through a Cursor's Result</title>
2830 There is a variant of the <command>FOR</> statement that allows
2831 iterating through the rows returned by a cursor. The syntax is:
2834 <optional> <<<replaceable>label</replaceable>>> </optional>
2835 FOR <replaceable>recordvar</replaceable> IN <replaceable>bound_cursor</replaceable> <optional> ( <replaceable>argument_values</replaceable> ) </optional> LOOP
2836 <replaceable>statements</replaceable>
2837 END LOOP <optional> <replaceable>label</replaceable> </optional>;
2840 The cursor variable must have been bound to some query when it was
2841 declared, and it <emphasis>cannot</> be open already. The
2842 <command>FOR</> statement automatically opens the cursor, and it closes
2843 the cursor again when the loop exits. A list of actual argument value
2844 expressions must appear if and only if the cursor was declared to take
2845 arguments. These values will be substituted in the query, in just
2846 the same way as during an <command>OPEN</>.
2847 The variable <replaceable>recordvar</replaceable> is automatically
2848 defined as type <type>record</> and exists only inside the loop (any
2849 existing definition of the variable name is ignored within the loop).
2850 Each row returned by the cursor is successively assigned to this
2851 record variable and the loop body is executed.
2857 <sect1 id="plpgsql-errors-and-messages">
2858 <title>Errors and Messages</title>
2861 <primary>RAISE</primary>
2865 <primary>reporting errors</primary>
2866 <secondary>in PL/PgSQL</secondary>
2870 Use the <command>RAISE</command> statement to report messages and
2874 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>;
2875 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>;
2876 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>;
2877 RAISE <optional> <replaceable class="parameter">level</replaceable> </optional> USING <replaceable class="parameter">option</replaceable> = <replaceable class="parameter">expression</replaceable> <optional>, ... </optional>;
2881 The <replaceable class="parameter">level</replaceable> option specifies
2882 the error severity. Allowed levels are <literal>DEBUG</literal>,
2883 <literal>LOG</literal>, <literal>INFO</literal>,
2884 <literal>NOTICE</literal>, <literal>WARNING</literal>,
2885 and <literal>EXCEPTION</literal>, with <literal>EXCEPTION</literal>
2887 <literal>EXCEPTION</literal> raises an error (which normally aborts the
2888 current transaction); the other levels only generate messages of different
2890 Whether messages of a particular priority are reported to the client,
2891 written to the server log, or both is controlled by the
2892 <xref linkend="guc-log-min-messages"> and
2893 <xref linkend="guc-client-min-messages"> configuration
2894 variables. See <xref linkend="runtime-config"> for more
2899 After <replaceable class="parameter">level</replaceable> if any,
2900 you can write a <replaceable class="parameter">format</replaceable>
2901 (which must be a simple string literal, not an expression). The
2902 format string specifies the error message text to be reported.
2903 The format string can be followed
2904 by optional argument expressions to be inserted into the message.
2905 Inside the format string, <literal>%</literal> is replaced by the
2906 string representation of the next optional argument's value. Write
2907 <literal>%%</literal> to emit a literal <literal>%</literal>.
2911 In this example, the value of <literal>v_job_id</> will replace the
2912 <literal>%</literal> in the string:
2914 RAISE NOTICE 'Calling cs_create_job(%)', v_job_id;
2919 You can attach additional information to the error report by writing
2920 <literal>USING</> followed by <replaceable
2921 class="parameter">option</replaceable> = <replaceable
2922 class="parameter">expression</replaceable> items. The allowed
2923 <replaceable class="parameter">option</replaceable> keywords are
2924 <literal>MESSAGE</>, <literal>DETAIL</>, <literal>HINT</>, and
2925 <literal>ERRCODE</>, while each <replaceable
2926 class="parameter">expression</replaceable> can be any string-valued
2928 <literal>MESSAGE</> sets the error message text (this option can't
2929 be used in the form of <command>RAISE</> that includes a format
2930 string before <literal>USING</>).
2931 <literal>DETAIL</> supplies an error detail message, while
2932 <literal>HINT</> supplies a hint message.
2933 <literal>ERRCODE</> specifies the error code (SQLSTATE) to report,
2934 either by condition name as shown in <xref linkend="errcodes-appendix">,
2935 or directly as a five-character SQLSTATE code.
2939 This example will abort the transaction with the given error message
2942 RAISE EXCEPTION 'Nonexistent ID --> %', user_id USING HINT = 'Please check your user id';
2947 These two examples show equivalent ways of setting the SQLSTATE:
2949 RAISE 'Duplicate user ID: %', user_id USING ERRCODE = 'unique_violation';
2950 RAISE 'Duplicate user ID: %', user_id USING ERRCODE = '23505';
2955 There is a second <command>RAISE</> syntax in which the main argument
2956 is the condition name or SQLSTATE to be reported, for example:
2958 RAISE division_by_zero;
2959 RAISE SQLSTATE '22012';
2961 In this syntax, <literal>USING</> can be used to supply a custom
2962 error message, detail, or hint. Another way to do the earlier
2965 RAISE unique_violation USING MESSAGE = 'Duplicate user ID: ' || user_id;
2970 Still another variant is to write <literal>RAISE USING</> or <literal>RAISE
2971 <replaceable class="parameter">level</replaceable> USING</> and put
2972 everything else into the <literal>USING</> list.
2976 The last variant of <command>RAISE</> has no parameters at all.
2977 This form can only be used inside a <literal>BEGIN</> block's
2978 <literal>EXCEPTION</> clause;
2979 it causes the error currently being handled to be re-thrown to the
2980 next enclosing block.
2984 If no condition name nor SQLSTATE is specified in a
2985 <command>RAISE EXCEPTION</command> command, the default is to use
2986 <literal>RAISE_EXCEPTION</> (<literal>P0001</>). If no message
2987 text is specified, the default is to use the condition name or
2988 SQLSTATE as message text.
2993 When specifying an error code by SQLSTATE code, you are not
2994 limited to the predefined error codes, but can select any
2995 error code consisting of five digits and/or upper-case ASCII
2996 letters, other than <literal>00000</>. It is recommended that
2997 you avoid throwing error codes that end in three zeroes, because
2998 these are category codes and can only be trapped by trapping
3005 <sect1 id="plpgsql-trigger">
3006 <title>Trigger Procedures</title>
3008 <indexterm zone="plpgsql-trigger">
3009 <primary>trigger</primary>
3010 <secondary>in PL/pgSQL</secondary>
3014 <application>PL/pgSQL</application> can be used to define trigger
3015 procedures. A trigger procedure is created with the
3016 <command>CREATE FUNCTION</> command, declaring it as a function with
3017 no arguments and a return type of <type>trigger</type>. Note that
3018 the function must be declared with no arguments even if it expects
3019 to receive arguments specified in <command>CREATE TRIGGER</> —
3020 trigger arguments are passed via <varname>TG_ARGV</>, as described
3025 When a <application>PL/pgSQL</application> function is called as a
3026 trigger, several special variables are created automatically in the
3027 top-level block. They are:
3031 <term><varname>NEW</varname></term>
3034 Data type <type>RECORD</type>; variable holding the new
3035 database row for <command>INSERT</>/<command>UPDATE</> operations in row-level
3036 triggers. This variable is <symbol>NULL</symbol> in statement-level triggers
3037 and for <command>DELETE</command> operations.
3043 <term><varname>OLD</varname></term>
3046 Data type <type>RECORD</type>; variable holding the old
3047 database row for <command>UPDATE</>/<command>DELETE</> operations in row-level
3048 triggers. This variable is <symbol>NULL</symbol> in statement-level triggers
3049 and for <command>INSERT</command> operations.
3055 <term><varname>TG_NAME</varname></term>
3058 Data type <type>name</type>; variable that contains the name of the trigger actually
3065 <term><varname>TG_WHEN</varname></term>
3068 Data type <type>text</type>; a string of either
3069 <literal>BEFORE</literal> or <literal>AFTER</literal>
3070 depending on the trigger's definition.
3076 <term><varname>TG_LEVEL</varname></term>
3079 Data type <type>text</type>; a string of either
3080 <literal>ROW</literal> or <literal>STATEMENT</literal>
3081 depending on the trigger's definition.
3087 <term><varname>TG_OP</varname></term>
3090 Data type <type>text</type>; a string of
3091 <literal>INSERT</literal>, <literal>UPDATE</literal>,
3092 <literal>DELETE</literal>, or <literal>TRUNCATE</>
3093 telling for which operation the trigger was fired.
3099 <term><varname>TG_RELID</varname></term>
3102 Data type <type>oid</type>; the object ID of the table that caused the
3109 <term><varname>TG_RELNAME</varname></term>
3112 Data type <type>name</type>; the name of the table that caused the trigger
3113 invocation. This is now deprecated, and could disappear in a future
3114 release. Use <literal>TG_TABLE_NAME</> instead.
3120 <term><varname>TG_TABLE_NAME</varname></term>
3123 Data type <type>name</type>; the name of the table that
3124 caused the trigger invocation.
3130 <term><varname>TG_TABLE_SCHEMA</varname></term>
3133 Data type <type>name</type>; the name of the schema of the
3134 table that caused the trigger invocation.
3140 <term><varname>TG_NARGS</varname></term>
3143 Data type <type>integer</type>; the number of arguments given to the trigger
3144 procedure in the <command>CREATE TRIGGER</command> statement.
3150 <term><varname>TG_ARGV[]</varname></term>
3153 Data type array of <type>text</type>; the arguments from
3154 the <command>CREATE TRIGGER</command> statement.
3155 The index counts from 0. Invalid
3156 indices (less than 0 or greater than or equal to <varname>tg_nargs</>) result in a null value.
3164 A trigger function must return either <symbol>NULL</symbol> or a
3165 record/row value having exactly the structure of the table the
3166 trigger was fired for.
3170 Row-level triggers fired <literal>BEFORE</> can return null to signal the
3171 trigger manager to skip the rest of the operation for this row
3172 (i.e., subsequent triggers are not fired, and the
3173 <command>INSERT</>/<command>UPDATE</>/<command>DELETE</> does not occur
3174 for this row). If a nonnull
3175 value is returned then the operation proceeds with that row value.
3176 Returning a row value different from the original value
3177 of <varname>NEW</> alters the row that will be inserted or updated
3178 (but has no direct effect in the <command>DELETE</> case).
3179 To alter the row to be stored, it is possible to replace single values
3180 directly in <varname>NEW</> and return the modified <varname>NEW</>,
3181 or to build a complete new record/row to return.
3185 The return value of a <literal>BEFORE</> or <literal>AFTER</>
3186 statement-level trigger or an <literal>AFTER</> row-level trigger is
3187 always ignored; it might as well be null. However, any of these types of
3188 triggers might still abort the entire operation by raising an error.
3192 <xref linkend="plpgsql-trigger-example"> shows an example of a
3193 trigger procedure in <application>PL/pgSQL</application>.
3196 <example id="plpgsql-trigger-example">
3197 <title>A <application>PL/pgSQL</application> Trigger Procedure</title>
3200 This example trigger ensures that any time a row is inserted or updated
3201 in the table, the current user name and time are stamped into the
3202 row. And it checks that an employee's name is given and that the
3203 salary is a positive value.
3210 last_date timestamp,
3214 CREATE FUNCTION emp_stamp() RETURNS trigger AS $emp_stamp$
3216 -- Check that empname and salary are given
3217 IF NEW.empname IS NULL THEN
3218 RAISE EXCEPTION 'empname cannot be null';
3220 IF NEW.salary IS NULL THEN
3221 RAISE EXCEPTION '% cannot have null salary', NEW.empname;
3224 -- Who works for us when she must pay for it?
3225 IF NEW.salary < 0 THEN
3226 RAISE EXCEPTION '% cannot have a negative salary', NEW.empname;
3229 -- Remember who changed the payroll when
3230 NEW.last_date := current_timestamp;
3231 NEW.last_user := current_user;
3234 $emp_stamp$ LANGUAGE plpgsql;
3236 CREATE TRIGGER emp_stamp BEFORE INSERT OR UPDATE ON emp
3237 FOR EACH ROW EXECUTE PROCEDURE emp_stamp();
3242 Another way to log changes to a table involves creating a new table that
3243 holds a row for each insert, update, or delete that occurs. This approach
3244 can be thought of as auditing changes to a table.
3245 <xref linkend="plpgsql-trigger-audit-example"> shows an example of an
3246 audit trigger procedure in <application>PL/pgSQL</application>.
3249 <example id="plpgsql-trigger-audit-example">
3250 <title>A <application>PL/pgSQL</application> Trigger Procedure For Auditing</title>
3253 This example trigger ensures that any insert, update or delete of a row
3254 in the <literal>emp</literal> table is recorded (i.e., audited) in the <literal>emp_audit</literal> table.
3255 The current time and user name are stamped into the row, together with
3256 the type of operation performed on it.
3261 empname text NOT NULL,
3265 CREATE TABLE emp_audit(
3266 operation char(1) NOT NULL,
3267 stamp timestamp NOT NULL,
3268 userid text NOT NULL,
3269 empname text NOT NULL,
3273 CREATE OR REPLACE FUNCTION process_emp_audit() RETURNS TRIGGER AS $emp_audit$
3276 -- Create a row in emp_audit to reflect the operation performed on emp,
3277 -- make use of the special variable TG_OP to work out the operation.
3279 IF (TG_OP = 'DELETE') THEN
3280 INSERT INTO emp_audit SELECT 'D', now(), user, OLD.*;
3282 ELSIF (TG_OP = 'UPDATE') THEN
3283 INSERT INTO emp_audit SELECT 'U', now(), user, NEW.*;
3285 ELSIF (TG_OP = 'INSERT') THEN
3286 INSERT INTO emp_audit SELECT 'I', now(), user, NEW.*;
3289 RETURN NULL; -- result is ignored since this is an AFTER trigger
3291 $emp_audit$ LANGUAGE plpgsql;
3293 CREATE TRIGGER emp_audit
3294 AFTER INSERT OR UPDATE OR DELETE ON emp
3295 FOR EACH ROW EXECUTE PROCEDURE process_emp_audit();
3300 One use of triggers is to maintain a summary table
3301 of another table. The resulting summary can be used in place of the
3302 original table for certain queries — often with vastly reduced run
3304 This technique is commonly used in Data Warehousing, where the tables
3305 of measured or observed data (called fact tables) might be extremely large.
3306 <xref linkend="plpgsql-trigger-summary-example"> shows an example of a
3307 trigger procedure in <application>PL/pgSQL</application> that maintains
3308 a summary table for a fact table in a data warehouse.
3312 <example id="plpgsql-trigger-summary-example">
3313 <title>A <application>PL/pgSQL</application> Trigger Procedure For Maintaining A Summary Table</title>
3316 The schema detailed here is partly based on the <emphasis>Grocery Store
3317 </emphasis> example from <emphasis>The Data Warehouse Toolkit</emphasis>
3323 -- Main tables - time dimension and sales fact.
3325 CREATE TABLE time_dimension (
3326 time_key integer NOT NULL,
3327 day_of_week integer NOT NULL,
3328 day_of_month integer NOT NULL,
3329 month integer NOT NULL,
3330 quarter integer NOT NULL,
3331 year integer NOT NULL
3333 CREATE UNIQUE INDEX time_dimension_key ON time_dimension(time_key);
3335 CREATE TABLE sales_fact (
3336 time_key integer NOT NULL,
3337 product_key integer NOT NULL,
3338 store_key integer NOT NULL,
3339 amount_sold numeric(12,2) NOT NULL,
3340 units_sold integer NOT NULL,
3341 amount_cost numeric(12,2) NOT NULL
3343 CREATE INDEX sales_fact_time ON sales_fact(time_key);
3346 -- Summary table - sales by time.
3348 CREATE TABLE sales_summary_bytime (
3349 time_key integer NOT NULL,
3350 amount_sold numeric(15,2) NOT NULL,
3351 units_sold numeric(12) NOT NULL,
3352 amount_cost numeric(15,2) NOT NULL
3354 CREATE UNIQUE INDEX sales_summary_bytime_key ON sales_summary_bytime(time_key);
3357 -- Function and trigger to amend summarized column(s) on UPDATE, INSERT, DELETE.
3359 CREATE OR REPLACE FUNCTION maint_sales_summary_bytime() RETURNS TRIGGER AS $maint_sales_summary_bytime$
3361 delta_time_key integer;
3362 delta_amount_sold numeric(15,2);
3363 delta_units_sold numeric(12);
3364 delta_amount_cost numeric(15,2);
3367 -- Work out the increment/decrement amount(s).
3368 IF (TG_OP = 'DELETE') THEN
3370 delta_time_key = OLD.time_key;
3371 delta_amount_sold = -1 * OLD.amount_sold;
3372 delta_units_sold = -1 * OLD.units_sold;
3373 delta_amount_cost = -1 * OLD.amount_cost;
3375 ELSIF (TG_OP = 'UPDATE') THEN
3377 -- forbid updates that change the time_key -
3378 -- (probably not too onerous, as DELETE + INSERT is how most
3379 -- changes will be made).
3380 IF ( OLD.time_key != NEW.time_key) THEN
3381 RAISE EXCEPTION 'Update of time_key : % -> % not allowed', OLD.time_key, NEW.time_key;
3384 delta_time_key = OLD.time_key;
3385 delta_amount_sold = NEW.amount_sold - OLD.amount_sold;
3386 delta_units_sold = NEW.units_sold - OLD.units_sold;
3387 delta_amount_cost = NEW.amount_cost - OLD.amount_cost;
3389 ELSIF (TG_OP = 'INSERT') THEN
3391 delta_time_key = NEW.time_key;
3392 delta_amount_sold = NEW.amount_sold;
3393 delta_units_sold = NEW.units_sold;
3394 delta_amount_cost = NEW.amount_cost;
3399 -- Insert or update the summary row with the new values.
3400 <<insert_update>>
3402 UPDATE sales_summary_bytime
3403 SET amount_sold = amount_sold + delta_amount_sold,
3404 units_sold = units_sold + delta_units_sold,
3405 amount_cost = amount_cost + delta_amount_cost
3406 WHERE time_key = delta_time_key;
3408 EXIT insert_update WHEN found;
3411 INSERT INTO sales_summary_bytime (
3426 WHEN UNIQUE_VIOLATION THEN
3429 END LOOP insert_update;
3434 $maint_sales_summary_bytime$ LANGUAGE plpgsql;
3436 CREATE TRIGGER maint_sales_summary_bytime
3437 AFTER INSERT OR UPDATE OR DELETE ON sales_fact
3438 FOR EACH ROW EXECUTE PROCEDURE maint_sales_summary_bytime();
3440 INSERT INTO sales_fact VALUES(1,1,1,10,3,15);
3441 INSERT INTO sales_fact VALUES(1,2,1,20,5,35);
3442 INSERT INTO sales_fact VALUES(2,2,1,40,15,135);
3443 INSERT INTO sales_fact VALUES(2,3,1,10,1,13);
3444 SELECT * FROM sales_summary_bytime;
3445 DELETE FROM sales_fact WHERE product_key = 1;
3446 SELECT * FROM sales_summary_bytime;
3447 UPDATE sales_fact SET units_sold = units_sold * 2;
3448 SELECT * FROM sales_summary_bytime;
3454 <sect1 id="plpgsql-implementation">
3455 <title><application>PL/pgSQL</> Under the Hood</title>
3458 This section discusses some implementation details that are
3459 frequently important for <application>PL/pgSQL</> users to know.
3462 <sect2 id="plpgsql-var-subst">
3463 <title>Variable Substitution</title>
3466 When <application>PL/pgSQL</> prepares a SQL statement or expression
3467 for execution, any <application>PL/pgSQL</application> variable name
3468 appearing in the statement or expression is replaced by a parameter symbol,
3469 <literal>$<replaceable>n</replaceable></literal>. The current value
3470 of the variable is then provided as the value for the parameter whenever
3471 the statement or expression is executed. As an example, consider the
3474 CREATE FUNCTION logfunc(logtxt text) RETURNS void AS $$
3476 curtime timestamp := now();
3478 INSERT INTO logtable VALUES (logtxt, curtime);
3480 $$ LANGUAGE plpgsql;
3482 The <command>INSERT</> statement will effectively be processed as
3484 PREPARE <replaceable>statement_name</>(text, timestamp) AS
3485 INSERT INTO logtable VALUES ($1, $2);
3487 followed on each execution by <command>EXECUTE</> with the current
3488 actual values of the two variables. (Note: here we are speaking of
3489 the main SQL engine's
3490 <xref linkend="sql-execute" endterm="sql-execute-title"> command,
3491 not <application>PL/pgSQL</application>'s <command>EXECUTE</>.)
3495 <emphasis>The substitution mechanism will replace any token that matches a
3496 known variable's name.</> This poses various traps for the unwary.
3497 For example, it is a bad idea
3498 to use a variable name that is the same as any table or column name
3499 that you need to reference in queries within the function, because
3500 what you think is a table or column name will still get replaced.
3501 In the above example, suppose that <structname>logtable</> has
3502 column names <structfield>logtxt</> and <structfield>logtime</>,
3503 and we try to write the <command>INSERT</> as
3505 INSERT INTO logtable (logtxt, logtime) VALUES (logtxt, curtime);
3507 This will be fed to the main SQL parser as
3509 INSERT INTO logtable ($1, logtime) VALUES ($1, $2);
3511 resulting in a syntax error like this:
3513 ERROR: syntax error at or near "$1"
3514 LINE 1: INSERT INTO logtable ( $1 , logtime) VALUES ( $1 , $2 )
3516 QUERY: INSERT INTO logtable ( $1 , logtime) VALUES ( $1 , $2 )
3517 CONTEXT: SQL statement in PL/PgSQL function "logfunc2" near line 5
3522 This example is fairly easy to diagnose, since it leads to an
3523 obvious syntax error. Much nastier are cases where the substitution
3524 is syntactically permissible, since the only symptom may be misbehavior
3525 of the function. In one case, a user wrote something like this:
3532 FOR val IN SELECT val FROM table WHERE key = search_key LOOP ...
3534 and wondered why all his table entries seemed to be NULL. Of course
3535 what happened here was that the query became
3537 SELECT $1 FROM table WHERE key = $2
3539 and thus it was just an expensive way of assigning <literal>val</>'s
3540 current value back to itself for each row.
3544 A commonly used coding rule for avoiding such traps is to use a
3545 different naming convention for <application>PL/pgSQL</application>
3546 variables than you use for table and column names. For example,
3547 if all your variables are named
3548 <literal>v_<replaceable>something</></literal> while none of your
3549 table or column names start with <literal>v_</>, you're pretty safe.
3553 Another workaround is to use qualified (dotted) names for SQL entities.
3554 For instance we could safely have written the above example as
3556 FOR val IN SELECT table.val FROM table WHERE key = search_key LOOP ...
3558 because <application>PL/pgSQL</application> will not substitute a
3559 variable for a trailing component of a qualified name.
3560 However this solution does not work in every case — you can't
3561 qualify a name in an <command>INSERT</>'s column name list, for instance.
3562 Another point is that record and row variable names will be matched to
3563 the first components of qualified names, so a qualified SQL name is
3564 still vulnerable in some cases.
3565 In such cases choosing a non-conflicting variable name is the only way.
3569 Another technique you can use is to attach a label to the block in
3570 which your variables are declared, and then qualify the variable names
3571 in your SQL commands (see <xref linkend="plpgsql-structure">).
3579 UPDATE table SET col = pl.val WHERE ...
3581 This is not in itself a solution to the problem of conflicts,
3582 since an unqualified name in a SQL command is still at risk of being
3583 interpreted the <quote>wrong</> way. But it is useful for clarifying
3584 the intent of potentially-ambiguous code.
3588 Variable substitution does not happen in the command string given
3589 to <command>EXECUTE</> or one of its variants. If you need to
3590 insert a varying value into such a command, do so as part of
3591 constructing the string value, as illustrated in
3592 <xref linkend="plpgsql-statements-executing-dyn">.
3596 Variable substitution currently works only in <command>SELECT</>,
3597 <command>INSERT</>, <command>UPDATE</>, and <command>DELETE</> commands,
3598 because the main SQL engine allows parameter symbols only in these
3599 commands. To use a non-constant name or value in other statement
3600 types (generically called utility statements), you must construct
3601 the utility statement as a string and <command>EXECUTE</> it.
3606 <sect2 id="plpgsql-plan-caching">
3607 <title>Plan Caching</title>
3610 The <application>PL/pgSQL</> interpreter parses the function's source
3611 text and produces an internal binary instruction tree the first time the
3612 function is called (within each session). The instruction tree
3613 fully translates the
3614 <application>PL/pgSQL</> statement structure, but individual
3615 <acronym>SQL</acronym> expressions and <acronym>SQL</acronym> commands
3616 used in the function are not translated immediately.
3620 As each expression and <acronym>SQL</acronym> command is first
3621 executed in the function, the <application>PL/pgSQL</> interpreter
3622 creates a prepared execution plan (using the
3623 <acronym>SPI</acronym> manager's <function>SPI_prepare</function>
3624 and <function>SPI_saveplan</function>
3625 functions).<indexterm><primary>preparing a query</><secondary>in
3626 PL/pgSQL</></> Subsequent visits to that expression or command
3627 reuse the prepared plan. Thus, a function with conditional code
3628 that contains many statements for which execution plans might be
3629 required will only prepare and save those plans that are really
3630 used during the lifetime of the database connection. This can
3631 substantially reduce the total amount of time required to parse
3632 and generate execution plans for the statements in a
3633 <application>PL/pgSQL</> function. A disadvantage is that errors
3634 in a specific expression or command cannot be detected until that
3635 part of the function is reached in execution. (Trivial syntax
3636 errors will be detected during the initial parsing pass, but
3637 anything deeper will not be detected until execution.)
3641 Once <application>PL/pgSQL</> has made an execution plan for a particular
3642 command in a function, it will reuse that plan for the life of the
3643 database connection. This is usually a win for performance, but it
3644 can cause some problems if you dynamically
3645 alter your database schema. For example:
3648 CREATE FUNCTION populate() RETURNS integer AS $$
3652 PERFORM my_function();
3654 $$ LANGUAGE plpgsql;
3657 If you execute the above function, it will reference the OID for
3658 <function>my_function()</function> in the execution plan produced for
3659 the <command>PERFORM</command> statement. Later, if you
3660 drop and recreate <function>my_function()</function>, then
3661 <function>populate()</function> will not be able to find
3662 <function>my_function()</function> anymore. You would then have to
3663 start a new database session so that <function>populate()</function>
3664 will be compiled afresh, before it will work again. You can avoid
3665 this problem by using <command>CREATE OR REPLACE FUNCTION</command>
3666 when updating the definition of
3667 <function>my_function</function>, since when a function is
3668 <quote>replaced</quote>, its OID is not changed.
3673 In <productname>PostgreSQL</productname> 8.3 and later, saved plans
3674 will be replaced whenever any schema changes have occurred to any
3675 tables they reference. This eliminates one of the major disadvantages
3676 of saved plans. However, there is no such mechanism for function
3677 references, and thus the above example involving a reference to a
3678 deleted function is still valid.
3683 Because <application>PL/pgSQL</application> saves execution plans
3684 in this way, SQL commands that appear directly in a
3685 <application>PL/pgSQL</application> function must refer to the
3686 same tables and columns on every execution; that is, you cannot use
3687 a parameter as the name of a table or column in an SQL command. To get
3688 around this restriction, you can construct dynamic commands using
3689 the <application>PL/pgSQL</application> <command>EXECUTE</command>
3690 statement — at the price of constructing a new execution plan on
3695 Another important point is that the prepared plans are parameterized
3696 to allow the values of <application>PL/pgSQL</application> variables
3697 to change from one use to the next, as discussed in detail above.
3698 Sometimes this means that a plan is less efficient than it would be
3699 if generated for a specific variable value. As an example, consider
3701 SELECT * INTO myrec FROM dictionary WHERE word LIKE search_term;
3703 where <literal>search_term</> is a <application>PL/pgSQL</application>
3704 variable. The cached plan for this query will never use an index on
3705 <structfield>word</>, since the planner cannot assume that the
3706 <literal>LIKE</> pattern will be left-anchored at run time. To use
3707 an index the query must be planned with a specific constant
3708 <literal>LIKE</> pattern provided. This is another situation where
3709 <command>EXECUTE</command> can be used to force a new plan to be
3710 generated for each execution.
3714 The mutable nature of record variables presents another problem in this
3715 connection. When fields of a record variable are used in
3716 expressions or statements, the data types of the fields must not
3717 change from one call of the function to the next, since each
3718 expression will be planned using the data type that is present
3719 when the expression is first reached. <command>EXECUTE</command> can be
3720 used to get around this problem when necessary.
3724 If the same function is used as a trigger for more than one table,
3725 <application>PL/pgSQL</application> prepares and caches plans
3726 independently for each such table — that is, there is a cache
3727 for each trigger function and table combination, not just for each
3728 function. This alleviates some of the problems with varying
3729 data types; for instance, a trigger function will be able to work
3730 successfully with a column named <literal>key</> even if it happens
3731 to have different types in different tables.
3735 Likewise, functions having polymorphic argument types have a separate
3736 plan cache for each combination of actual argument types they have been
3737 invoked for, so that data type differences do not cause unexpected
3742 Plan caching can sometimes have surprising effects on the interpretation
3743 of time-sensitive values. For example there
3744 is a difference between what these two functions do:
3747 CREATE FUNCTION logfunc1(logtxt text) RETURNS void AS $$
3749 INSERT INTO logtable VALUES (logtxt, 'now');
3751 $$ LANGUAGE plpgsql;
3757 CREATE FUNCTION logfunc2(logtxt text) RETURNS void AS $$
3762 INSERT INTO logtable VALUES (logtxt, curtime);
3764 $$ LANGUAGE plpgsql;
3769 In the case of <function>logfunc1</function>, the
3770 <productname>PostgreSQL</productname> main parser knows when
3771 preparing the plan for the <command>INSERT</command> that the
3772 string <literal>'now'</literal> should be interpreted as
3773 <type>timestamp</type>, because the target column of
3774 <classname>logtable</classname> is of that type. Thus,
3775 <literal>'now'</literal> will be converted to a constant when the
3776 <command>INSERT</command> is planned, and then used in all
3777 invocations of <function>logfunc1</function> during the lifetime
3778 of the session. Needless to say, this isn't what the programmer
3783 In the case of <function>logfunc2</function>, the
3784 <productname>PostgreSQL</productname> main parser does not know
3785 what type <literal>'now'</literal> should become and therefore
3786 it returns a data value of type <type>text</type> containing the string
3787 <literal>now</literal>. During the ensuing assignment
3788 to the local variable <varname>curtime</varname>, the
3789 <application>PL/pgSQL</application> interpreter casts this
3790 string to the <type>timestamp</type> type by calling the
3791 <function>text_out</function> and <function>timestamp_in</function>
3792 functions for the conversion. So, the computed time stamp is updated
3793 on each execution as the programmer expects.
3800 <sect1 id="plpgsql-development-tips">
3801 <title>Tips for Developing in <application>PL/pgSQL</application></title>
3804 One good way to develop in
3805 <application>PL/pgSQL</> is to use the text editor of your
3806 choice to create your functions, and in another window, use
3807 <application>psql</application> to load and test those functions.
3808 If you are doing it this way, it
3809 is a good idea to write the function using <command>CREATE OR
3810 REPLACE FUNCTION</>. That way you can just reload the file to update
3811 the function definition. For example:
3813 CREATE OR REPLACE FUNCTION testfunc(integer) RETURNS integer AS $$
3815 $$ LANGUAGE plpgsql;
3820 While running <application>psql</application>, you can load or reload such
3821 a function definition file with:
3825 and then immediately issue SQL commands to test the function.
3829 Another good way to develop in <application>PL/pgSQL</> is with a
3830 GUI database access tool that facilitates development in a
3831 procedural language. One example of such as a tool is
3832 <application>pgAdmin</>, although others exist. These tools often
3833 provide convenient features such as escaping single quotes and
3834 making it easier to recreate and debug functions.
3837 <sect2 id="plpgsql-quote-tips">
3838 <title>Handling of Quotation Marks</title>
3841 The code of a <application>PL/pgSQL</> function is specified in
3842 <command>CREATE FUNCTION</command> as a string literal. If you
3843 write the string literal in the ordinary way with surrounding
3844 single quotes, then any single quotes inside the function body
3845 must be doubled; likewise any backslashes must be doubled (assuming
3846 escape string syntax is used).
3847 Doubling quotes is at best tedious, and in more complicated cases
3848 the code can become downright incomprehensible, because you can
3849 easily find yourself needing half a dozen or more adjacent quote marks.
3850 It's recommended that you instead write the function body as a
3851 <quote>dollar-quoted</> string literal (see <xref
3852 linkend="sql-syntax-dollar-quoting">). In the dollar-quoting
3853 approach, you never double any quote marks, but instead take care to
3854 choose a different dollar-quoting delimiter for each level of
3855 nesting you need. For example, you might write the <command>CREATE
3856 FUNCTION</command> command as:
3858 CREATE OR REPLACE FUNCTION testfunc(integer) RETURNS integer AS $PROC$
3860 $PROC$ LANGUAGE plpgsql;
3862 Within this, you might use quote marks for simple literal strings in
3863 SQL commands and <literal>$$</> to delimit fragments of SQL commands
3864 that you are assembling as strings. If you need to quote text that
3865 includes <literal>$$</>, you could use <literal>$Q$</>, and so on.
3869 The following chart shows what you have to do when writing quote
3870 marks without dollar quoting. It might be useful when translating
3871 pre-dollar quoting code into something more comprehensible.
3876 <term>1 quotation mark</term>
3879 To begin and end the function body, for example:
3881 CREATE FUNCTION foo() RETURNS integer AS '
3885 Anywhere within a single-quoted function body, quote marks
3886 <emphasis>must</> appear in pairs.
3892 <term>2 quotation marks</term>
3895 For string literals inside the function body, for example:
3897 a_output := ''Blah'';
3898 SELECT * FROM users WHERE f_name=''foobar'';
3900 In the dollar-quoting approach, you'd just write:
3903 SELECT * FROM users WHERE f_name='foobar';
3905 which is exactly what the <application>PL/pgSQL</> parser would see
3912 <term>4 quotation marks</term>
3915 When you need a single quotation mark in a string constant inside the
3916 function body, for example:
3918 a_output := a_output || '' AND name LIKE ''''foobar'''' AND xyz''
3920 The value actually appended to <literal>a_output</literal> would be:
3921 <literal> AND name LIKE 'foobar' AND xyz</literal>.
3924 In the dollar-quoting approach, you'd write:
3926 a_output := a_output || $$ AND name LIKE 'foobar' AND xyz$$
3928 being careful that any dollar-quote delimiters around this are not
3929 just <literal>$$</>.
3935 <term>6 quotation marks</term>
3938 When a single quotation mark in a string inside the function body is
3939 adjacent to the end of that string constant, for example:
3941 a_output := a_output || '' AND name LIKE ''''foobar''''''
3943 The value appended to <literal>a_output</literal> would then be:
3944 <literal> AND name LIKE 'foobar'</literal>.
3947 In the dollar-quoting approach, this becomes:
3949 a_output := a_output || $$ AND name LIKE 'foobar'$$
3956 <term>10 quotation marks</term>
3959 When you want two single quotation marks in a string constant (which
3960 accounts for 8 quotation marks) and this is adjacent to the end of that
3961 string constant (2 more). You will probably only need that if
3962 you are writing a function that generates other functions, as in
3963 <xref linkend="plpgsql-porting-ex2">.
3966 a_output := a_output || '' if v_'' ||
3967 referrer_keys.kind || '' like ''''''''''
3968 || referrer_keys.key_string || ''''''''''
3969 then return '''''' || referrer_keys.referrer_type
3970 || ''''''; end if;'';
3972 The value of <literal>a_output</literal> would then be:
3974 if v_... like ''...'' then return ''...''; end if;
3978 In the dollar-quoting approach, this becomes:
3980 a_output := a_output || $$ if v_$$ || referrer_keys.kind || $$ like '$$
3981 || referrer_keys.key_string || $$'
3982 then return '$$ || referrer_keys.referrer_type
3985 where we assume we only need to put single quote marks into
3986 <literal>a_output</literal>, because it will be re-quoted before use.
3995 <!-- **** Porting from Oracle PL/SQL **** -->
3997 <sect1 id="plpgsql-porting">
3998 <title>Porting from <productname>Oracle</productname> PL/SQL</title>
4000 <indexterm zone="plpgsql-porting">
4001 <primary>Oracle</primary>
4002 <secondary>porting from PL/SQL to PL/pgSQL</secondary>
4005 <indexterm zone="plpgsql-porting">
4006 <primary>PL/SQL (Oracle)</primary>
4007 <secondary>porting to PL/pgSQL</secondary>
4011 This section explains differences between
4012 <productname>PostgreSQL</>'s <application>PL/pgSQL</application>
4013 language and Oracle's <application>PL/SQL</application> language,
4014 to help developers who port applications from
4015 <trademark class="registered">Oracle</> to <productname>PostgreSQL</>.
4019 <application>PL/pgSQL</application> is similar to PL/SQL in many
4020 aspects. It is a block-structured, imperative language, and all
4021 variables have to be declared. Assignments, loops, conditionals
4022 are similar. The main differences you should keep in mind when
4023 porting from <application>PL/SQL</> to
4024 <application>PL/pgSQL</application> are:
4029 There are no default values for parameters in <productname>PostgreSQL</>.
4035 You can overload function names in <productname>PostgreSQL</>. This is
4036 often used to work around the lack of default parameters.
4042 If a name used in a SQL command could be either a column name of a
4043 table or a reference to a variable of the function,
4044 <application>PL/SQL</> treats it as a column name, while
4045 <application>PL/pgSQL</> treats it as a variable name. It's best
4046 to avoid such ambiguities in the first place, but if necessary you
4047 can fix them by properly qualifying the ambiguous name.
4048 (See <xref linkend="plpgsql-var-subst">.)
4054 In <productname>PostgreSQL</> the function body must be written as
4055 a string literal. Therefore you need to use dollar quoting or escape
4056 single quotes in the function body. (See <xref
4057 linkend="plpgsql-quote-tips">.)
4063 Instead of packages, use schemas to organize your functions
4070 Since there are no packages, there are no package-level variables
4071 either. This is somewhat annoying. You can keep per-session state
4072 in temporary tables instead.
4078 Integer <command>FOR</> loops with <literal>REVERSE</> work
4079 differently: <application>PL/SQL</> counts down from the second
4080 number to the first, while <application>PL/pgSQL</> counts down
4081 from the first number to the second, requiring the loop bounds
4082 to be swapped when porting. This incompatibility is unfortunate
4083 but is unlikely to be changed. (See <xref
4084 linkend="plpgsql-integer-for">.)
4090 <command>FOR</> loops over queries (other than cursors) also work
4091 differently: the target variable(s) must have been declared,
4092 whereas <application>PL/SQL</> always declares them implicitly.
4093 An advantage of this is that the variable values are still accessible
4094 after the loop exits.
4100 There are various notational differences for the use of cursor
4109 <title>Porting Examples</title>
4112 <xref linkend="pgsql-porting-ex1"> shows how to port a simple
4113 function from <application>PL/SQL</> to <application>PL/pgSQL</>.
4116 <example id="pgsql-porting-ex1">
4117 <title>Porting a Simple Function from <application>PL/SQL</> to <application>PL/pgSQL</></title>
4120 Here is an <productname>Oracle</productname> <application>PL/SQL</> function:
4122 CREATE OR REPLACE FUNCTION cs_fmt_browser_version(v_name varchar,
4126 IF v_version IS NULL THEN
4129 RETURN v_name || '/' || v_version;
4137 Let's go through this function and see the differences compared to
4138 <application>PL/pgSQL</>:
4143 The <literal>RETURN</literal> key word in the function
4144 prototype (not the function body) becomes
4145 <literal>RETURNS</literal> in
4146 <productname>PostgreSQL</productname>.
4147 Also, <literal>IS</> becomes <literal>AS</>, and you need to
4148 add a <literal>LANGUAGE</> clause because <application>PL/pgSQL</>
4149 is not the only possible function language.
4155 In <productname>PostgreSQL</>, the function body is considered
4156 to be a string literal, so you need to use quote marks or dollar
4157 quotes around it. This substitutes for the terminating <literal>/</>
4158 in the Oracle approach.
4164 The <literal>show errors</literal> command does not exist in
4165 <productname>PostgreSQL</>, and is not needed since errors are
4166 reported automatically.
4173 This is how this function would look when ported to
4174 <productname>PostgreSQL</>:
4177 CREATE OR REPLACE FUNCTION cs_fmt_browser_version(v_name varchar,
4179 RETURNS varchar AS $$
4181 IF v_version IS NULL THEN
4184 RETURN v_name || '/' || v_version;
4186 $$ LANGUAGE plpgsql;
4192 <xref linkend="plpgsql-porting-ex2"> shows how to port a
4193 function that creates another function and how to handle the
4194 ensuing quoting problems.
4197 <example id="plpgsql-porting-ex2">
4198 <title>Porting a Function that Creates Another Function from <application>PL/SQL</> to <application>PL/pgSQL</></title>
4201 The following procedure grabs rows from a
4202 <command>SELECT</command> statement and builds a large function
4203 with the results in <literal>IF</literal> statements, for the
4208 This is the Oracle version:
4210 CREATE OR REPLACE PROCEDURE cs_update_referrer_type_proc IS
4211 CURSOR referrer_keys IS
4212 SELECT * FROM cs_referrer_keys
4214 func_cmd VARCHAR(4000);
4216 func_cmd := 'CREATE OR REPLACE FUNCTION cs_find_referrer_type(v_host IN VARCHAR,
4217 v_domain IN VARCHAR, v_url IN VARCHAR) RETURN VARCHAR IS BEGIN';
4219 FOR referrer_key IN referrer_keys LOOP
4220 func_cmd := func_cmd ||
4221 ' IF v_' || referrer_key.kind
4222 || ' LIKE ''' || referrer_key.key_string
4223 || ''' THEN RETURN ''' || referrer_key.referrer_type
4227 func_cmd := func_cmd || ' RETURN NULL; END;';
4229 EXECUTE IMMEDIATE func_cmd;
4237 Here is how this function would end up in <productname>PostgreSQL</>:
4239 CREATE OR REPLACE FUNCTION cs_update_referrer_type_proc() RETURNS void AS $func$
4241 CURSOR referrer_keys IS
4242 SELECT * FROM cs_referrer_keys
4247 func_body := 'BEGIN';
4249 FOR referrer_key IN referrer_keys LOOP
4250 func_body := func_body ||
4251 ' IF v_' || referrer_key.kind
4252 || ' LIKE ' || quote_literal(referrer_key.key_string)
4253 || ' THEN RETURN ' || quote_literal(referrer_key.referrer_type)
4257 func_body := func_body || ' RETURN NULL; END;';
4260 'CREATE OR REPLACE FUNCTION cs_find_referrer_type(v_host varchar,
4263 RETURNS varchar AS '
4264 || quote_literal(func_body)
4265 || ' LANGUAGE plpgsql;' ;
4269 $func$ LANGUAGE plpgsql;
4271 Notice how the body of the function is built separately and passed
4272 through <literal>quote_literal</> to double any quote marks in it. This
4273 technique is needed because we cannot safely use dollar quoting for
4274 defining the new function: we do not know for sure what strings will
4275 be interpolated from the <structfield>referrer_key.key_string</> field.
4276 (We are assuming here that <structfield>referrer_key.kind</> can be
4277 trusted to always be <literal>host</>, <literal>domain</>, or
4278 <literal>url</>, but <structfield>referrer_key.key_string</> might be
4279 anything, in particular it might contain dollar signs.) This function
4280 is actually an improvement on the Oracle original, because it will
4281 not generate broken code when <structfield>referrer_key.key_string</> or
4282 <structfield>referrer_key.referrer_type</> contain quote marks.
4287 <xref linkend="plpgsql-porting-ex3"> shows how to port a function
4288 with <literal>OUT</> parameters and string manipulation.
4289 <productname>PostgreSQL</> does not have a built-in
4290 <function>instr</function> function, but you can create one
4291 using a combination of other
4292 functions.<indexterm><primary>instr</></indexterm> In <xref
4293 linkend="plpgsql-porting-appendix"> there is a
4294 <application>PL/pgSQL</application> implementation of
4295 <function>instr</function> that you can use to make your porting
4299 <example id="plpgsql-porting-ex3">
4300 <title>Porting a Procedure With String Manipulation and
4301 <literal>OUT</> Parameters from <application>PL/SQL</> to
4302 <application>PL/pgSQL</></title>
4305 The following <productname>Oracle</productname> PL/SQL procedure is used
4306 to parse a URL and return several elements (host, path, and query).
4310 This is the Oracle version:
4312 CREATE OR REPLACE PROCEDURE cs_parse_url(
4314 v_host OUT VARCHAR, -- This will be passed back
4315 v_path OUT VARCHAR, -- This one too
4316 v_query OUT VARCHAR) -- And this one
4324 a_pos1 := instr(v_url, '//');
4329 a_pos2 := instr(v_url, '/', a_pos1 + 2);
4331 v_host := substr(v_url, a_pos1 + 2);
4336 v_host := substr(v_url, a_pos1 + 2, a_pos2 - a_pos1 - 2);
4337 a_pos1 := instr(v_url, '?', a_pos2 + 1);
4340 v_path := substr(v_url, a_pos2);
4344 v_path := substr(v_url, a_pos2, a_pos1 - a_pos2);
4345 v_query := substr(v_url, a_pos1 + 1);
4353 Here is a possible translation into <application>PL/pgSQL</>:
4355 CREATE OR REPLACE FUNCTION cs_parse_url(
4357 v_host OUT VARCHAR, -- This will be passed back
4358 v_path OUT VARCHAR, -- This one too
4359 v_query OUT VARCHAR) -- And this one
4368 a_pos1 := instr(v_url, '//');
4373 a_pos2 := instr(v_url, '/', a_pos1 + 2);
4375 v_host := substr(v_url, a_pos1 + 2);
4380 v_host := substr(v_url, a_pos1 + 2, a_pos2 - a_pos1 - 2);
4381 a_pos1 := instr(v_url, '?', a_pos2 + 1);
4384 v_path := substr(v_url, a_pos2);
4388 v_path := substr(v_url, a_pos2, a_pos1 - a_pos2);
4389 v_query := substr(v_url, a_pos1 + 1);
4391 $$ LANGUAGE plpgsql;
4394 This function could be used like this:
4396 SELECT * FROM cs_parse_url('http://foobar.com/query.cgi?baz');
4402 <xref linkend="plpgsql-porting-ex4"> shows how to port a procedure
4403 that uses numerous features that are specific to Oracle.
4406 <example id="plpgsql-porting-ex4">
4407 <title>Porting a Procedure from <application>PL/SQL</> to <application>PL/pgSQL</></title>
4413 CREATE OR REPLACE PROCEDURE cs_create_job(v_job_id IN INTEGER) IS
4414 a_running_job_count INTEGER;
4415 PRAGMA AUTONOMOUS_TRANSACTION;<co id="co.plpgsql-porting-pragma">
4417 LOCK TABLE cs_jobs IN EXCLUSIVE MODE;<co id="co.plpgsql-porting-locktable">
4419 SELECT count(*) INTO a_running_job_count FROM cs_jobs WHERE end_stamp IS NULL;
4421 IF a_running_job_count > 0 THEN
4422 COMMIT; -- free lock<co id="co.plpgsql-porting-commit">
4423 raise_application_error(-20000, 'Unable to create a new job: a job is currently running.');
4426 DELETE FROM cs_active_job;
4427 INSERT INTO cs_active_job(job_id) VALUES (v_job_id);
4430 INSERT INTO cs_jobs (job_id, start_stamp) VALUES (v_job_id, sysdate);
4432 WHEN dup_val_on_index THEN NULL; -- don't worry if it already exists
4442 Procedures like this can easily be converted into <productname>PostgreSQL</>
4443 functions returning <type>void</type>. This procedure in
4444 particular is interesting because it can teach us some things:
4447 <callout arearefs="co.plpgsql-porting-pragma">
4449 There is no <literal>PRAGMA</literal> statement in <productname>PostgreSQL</>.
4453 <callout arearefs="co.plpgsql-porting-locktable">
4455 If you do a <command>LOCK TABLE</command> in <application>PL/pgSQL</>,
4456 the lock will not be released until the calling transaction is
4461 <callout arearefs="co.plpgsql-porting-commit">
4463 You cannot issue <command>COMMIT</> in a
4464 <application>PL/pgSQL</application> function. The function is
4465 running within some outer transaction and so <command>COMMIT</>
4466 would imply terminating the function's execution. However, in
4467 this particular case it is not necessary anyway, because the lock
4468 obtained by the <command>LOCK TABLE</command> will be released when
4476 This is how we could port this procedure to <application>PL/pgSQL</>:
4479 CREATE OR REPLACE FUNCTION cs_create_job(v_job_id integer) RETURNS void AS $$
4481 a_running_job_count integer;
4483 LOCK TABLE cs_jobs IN EXCLUSIVE MODE;
4485 SELECT count(*) INTO a_running_job_count FROM cs_jobs WHERE end_stamp IS NULL;
4487 IF a_running_job_count > 0 THEN
4488 RAISE EXCEPTION 'Unable to create a new job: a job is currently running';<co id="co.plpgsql-porting-raise">
4491 DELETE FROM cs_active_job;
4492 INSERT INTO cs_active_job(job_id) VALUES (v_job_id);
4495 INSERT INTO cs_jobs (job_id, start_stamp) VALUES (v_job_id, now());
4497 WHEN unique_violation THEN <co id="co.plpgsql-porting-exception">
4498 -- don't worry if it already exists
4501 $$ LANGUAGE plpgsql;
4505 <callout arearefs="co.plpgsql-porting-raise">
4507 The syntax of <literal>RAISE</> is considerably different from
4508 Oracle's statement, although the basic case <literal>RAISE</>
4509 <replaceable class="parameter">exception_name</replaceable> works
4513 <callout arearefs="co.plpgsql-porting-exception">
4515 The exception names supported by <application>PL/pgSQL</> are
4516 different from Oracle's. The set of built-in exception names
4517 is much larger (see <xref linkend="errcodes-appendix">). There
4518 is not currently a way to declare user-defined exception names.
4523 The main functional difference between this procedure and the
4524 Oracle equivalent is that the exclusive lock on the <literal>cs_jobs</>
4525 table will be held until the calling transaction completes. Also, if
4526 the caller later aborts (for example due to an error), the effects of
4527 this procedure will be rolled back.
4532 <sect2 id="plpgsql-porting-other">
4533 <title>Other Things to Watch For</title>
4536 This section explains a few other things to watch for when porting
4537 Oracle <application>PL/SQL</> functions to
4538 <productname>PostgreSQL</productname>.
4541 <sect3 id="plpgsql-porting-exceptions">
4542 <title>Implicit Rollback after Exceptions</title>
4545 In <application>PL/pgSQL</>, when an exception is caught by an
4546 <literal>EXCEPTION</> clause, all database changes since the block's
4547 <literal>BEGIN</> are automatically rolled back. That is, the behavior
4548 is equivalent to what you'd get in Oracle with:
4564 If you are translating an Oracle procedure that uses
4565 <command>SAVEPOINT</> and <command>ROLLBACK TO</> in this style,
4566 your task is easy: just omit the <command>SAVEPOINT</> and
4567 <command>ROLLBACK TO</>. If you have a procedure that uses
4568 <command>SAVEPOINT</> and <command>ROLLBACK TO</> in a different way
4569 then some actual thought will be required.
4574 <title><command>EXECUTE</command></title>
4577 The <application>PL/pgSQL</> version of
4578 <command>EXECUTE</command> works similarly to the
4579 <application>PL/SQL</> version, but you have to remember to use
4580 <function>quote_literal</function> and
4581 <function>quote_ident</function> as described in <xref
4582 linkend="plpgsql-statements-executing-dyn">. Constructs of the
4583 type <literal>EXECUTE 'SELECT * FROM $1';</literal> will not work
4584 reliably unless you use these functions.
4588 <sect3 id="plpgsql-porting-optimization">
4589 <title>Optimizing <application>PL/pgSQL</application> Functions</title>
4592 <productname>PostgreSQL</> gives you two function creation
4593 modifiers to optimize execution: <quote>volatility</> (whether
4594 the function always returns the same result when given the same
4595 arguments) and <quote>strictness</quote> (whether the function
4596 returns null if any argument is null). Consult the <xref
4597 linkend="sql-createfunction" endterm="sql-createfunction-title">
4598 reference page for details.
4602 When making use of these optimization attributes, your
4603 <command>CREATE FUNCTION</command> statement might look something
4607 CREATE FUNCTION foo(...) RETURNS integer AS $$
4609 $$ LANGUAGE plpgsql STRICT IMMUTABLE;
4615 <sect2 id="plpgsql-porting-appendix">
4616 <title>Appendix</title>
4619 This section contains the code for a set of Oracle-compatible
4620 <function>instr</function> functions that you can use to simplify
4621 your porting efforts.
4626 -- instr functions that mimic Oracle's counterpart
4627 -- Syntax: instr(string1, string2, [n], [m]) where [] denotes optional parameters.
4629 -- Searches string1 beginning at the nth character for the mth occurrence
4630 -- of string2. If n is negative, search backwards. If m is not passed,
4631 -- assume 1 (search starts at first character).
4634 CREATE FUNCTION instr(varchar, varchar) RETURNS integer AS $$
4638 pos:= instr($1, $2, 1);
4641 $$ LANGUAGE plpgsql STRICT IMMUTABLE;
4644 CREATE FUNCTION instr(string varchar, string_to_search varchar, beg_index integer)
4645 RETURNS integer AS $$
4647 pos integer NOT NULL DEFAULT 0;
4653 IF beg_index > 0 THEN
4654 temp_str := substring(string FROM beg_index);
4655 pos := position(string_to_search IN temp_str);
4660 RETURN pos + beg_index - 1;
4663 ss_length := char_length(string_to_search);
4664 length := char_length(string);
4665 beg := length + beg_index - ss_length + 2;
4667 WHILE beg > 0 LOOP
4668 temp_str := substring(string FROM beg FOR ss_length);
4669 pos := position(string_to_search IN temp_str);
4681 $$ LANGUAGE plpgsql STRICT IMMUTABLE;
4684 CREATE FUNCTION instr(string varchar, string_to_search varchar,
4685 beg_index integer, occur_index integer)
4686 RETURNS integer AS $$
4688 pos integer NOT NULL DEFAULT 0;
4689 occur_number integer NOT NULL DEFAULT 0;
4696 IF beg_index > 0 THEN
4698 temp_str := substring(string FROM beg_index);
4700 FOR i IN 1..occur_index LOOP
4701 pos := position(string_to_search IN temp_str);
4704 beg := beg + pos - 1;
4709 temp_str := substring(string FROM beg + 1);
4718 ss_length := char_length(string_to_search);
4719 length := char_length(string);
4720 beg := length + beg_index - ss_length + 2;
4722 WHILE beg > 0 LOOP
4723 temp_str := substring(string FROM beg FOR ss_length);
4724 pos := position(string_to_search IN temp_str);
4727 occur_number := occur_number + 1;
4729 IF occur_number = occur_index THEN
4740 $$ LANGUAGE plpgsql STRICT IMMUTABLE;