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<chapter id="syntax">
<tip>
<para>
- Any string can be specified as an identifier if surrounded by
+ Any string can be used as an identifier if surrounded by
double quotes (<quote>like this!</quote>). Some care is required since
such an identifier will be case sensitive
and will retain embedded whitespace and most other special characters.
</programlisting>
where the comment begins with "<literal>/*</literal>" and extends
- to the first occurrence of "<literal>*/</literal>". These block
+ to the matching occurrence of "<literal>*/</literal>". These block
comments nest, as specified in SQL99, so that one can comment out
larger blocks of code which may contain existing block comments.
</para>
truncated.
By default, NAMEDATALEN is 32 so the maximum name length is 31 (but
at the time the system is built, NAMEDATALEN can be changed in
- src/include/postgres_ext.h).
+ <filename>src/include/postgres_ext.h</filename>).
</para>
<para>
<title>Constants</title>
<para>
- There are three <firstterm>implicitly typed constants</firstterm>
-
for use in <productname>Postgres</productname>: strings, integers,
+ There are three kinds of <firstterm>implicitly typed constants</firstterm>
+ in <productname>Postgres</productname>: strings, integers,
and floating point numbers. Constants can
also be specified with explicit types, which can enable more
accurate representation and more efficient handling by the
<para>
<firstterm>Integer constants</firstterm>
- in SQL are collection of ASCII digits with no decimal point. Legal
- values range from -2147483648 to +2147483647. This will vary
- depending on the operating system and host machine.
- </para>
-
- <para>
- Note that larger integers can be specified for <type>int8</type>
- by using <acronym>SQL92</acronym> string notation or
- <productname>Postgres</productname> type notation:
-
- <programlisting>
-int8 '4000000000' -- string style
-'4000000000'::int8 -- Postgres (historical) style
- </programlisting>
+ in SQL are sequences of ASCII digits with no decimal point.
+ The range of legal values depends on which integer datatype is
+ used, but the plain <literal>integer</literal> type accepts values
+ ranging from -2147483648 to +2147483647.
</para>
</sect2>
if there is no ambiguity as to the type the constant must be, in which
case it is automatically coerced.
</para>
+
+ <para>
+ It is also possible to specify a type coercion using a function-like
+ syntax:
+
+ <synopsis>
+<replaceable>typename</replaceable> ( <replaceable>value</replaceable> )
+ </synopsis>
+
+ although this only works for types whose names are also valid as
+ function names. (For example, <literal>double precision</literal>
+ can't be used this way --- but the equivalent <literal>float8</literal>
+ can.)
+ </para>
+
+ <para>
+ The <literal>::</literal>, <literal>CAST()</literal>, and function-call
+ syntaxes can also be used to specify run-time type conversions. But
+ the form <replaceable>type</replaceable>
+ '<replaceable>string</replaceable>' can only be used to specify the
+ type of a literal constant.
+ </para>
</sect2>
<sect2>
<para>
<firstterm>Array constants</firstterm>
- are arrays of any Postgres type, including other arrays, string
- constants, etc. The general format of an array constant is the
- following:
+ are n-dimensional arrays of any Postgres datatype.
+ The general format of an array constant is the following:
<synopsis>
-{<replaceable>val1</replaceable><replaceable>delim</replaceable><replaceable>val2</replaceable><replaceable>delim</replaceable>}
+{ <replaceable>val1</replaceable> <replaceable>delim</replaceable> <replaceable>val2</replaceable> <replaceable>delim</replaceable> ... }
</synopsis>
where <replaceable>delim</replaceable>
- is the delimiter for the type stored in the <literal>pg_type</literal> class.
- (For built-in types, this is the comma character (","). An
- example of an array constant is
+ is the delimiter character for the type, as recorded in its
+ <literal>pg_type</literal> class entry.
+ (For all built-in types, this is the comma character ",".)
+ Each <replaceable>val</replaceable> is either a constant
+ of the array element type, or a sub-array.
+ An example of an array constant is
<programlisting>
{{1,2,3},{4,5,6},{7,8,9}}
</para>
<para>
- Individual array elements can and should be placed between quotation
- marks whenever possible to avoid ambiguity problems with respect to
- leading white space.
+ Individual array elements can be placed between single-quote
+ marks to avoid ambiguity problems with respect to leading white space.
+ Without quote marks, the array-value parser will skip white space.
+ Note that to write a quote mark inside a string literal that is to
+ become an array value, you must double the quote mark as described
+ previously.
</para>
</sect2>
</sect1>
<para>
A <firstterm>field</firstterm>
- is either an attribute of a given class or one of the following:
+ is either a user-defined attribute of a given class or one of the
+ following system-defined attributes:
<variablelist>
<varlistentry>
<listitem>
<para>
stands for the unique identifier of an instance which is added by
- Postgres to all instances automatically. Oids are not reused and are 32
- bit quantities.
+ Postgres to all instances automatically. OIDs are not reused and are
+ 32-bit quantities.
</para>
</listitem>
</varlistentry>
<term>cmin</term>
<listitem>
<para>
- The command identifier within the transaction.
+ The command identifier within the inserting transaction.
</para>
</listitem>
</varlistentry>
<term>cmax</term>
<listitem>
<para>
- The identity of the deleting command.
+ The command identifier within the deleting transaction.
</para>
</listitem>
</varlistentry>
</para>
<para>
- For further information on these fields consult
+ For further information on the system attributes consult
<xref linkend="STON87a" endterm="STON87a">.
- Times are represented internally as instances of the
- <literal>abstime</literal>
- data type. Transaction and command identifiers are 32 bit quantities.
- Transactions are assigned sequentially starting at 512.
+ Transaction and command identifiers are 32 bit quantities.
</para>
</sect2>
A <firstterm>column</firstterm> is a construct of the form:
<synopsis>
-<replaceable>instance</replaceable>{.<replaceable>composite_field</replaceable>}.<replaceable>field</replaceable> `['<replaceable>number</replaceable>`]'
+<replaceable>instance</replaceable>{.<replaceable>composite_field</replaceable>}.<replaceable>field</replaceable> `['<replaceable>subscript</replaceable>`]'
</synopsis>
<replaceable>instance</replaceable>
identifies a particular class and can be thought of as standing for
the instances of that class. An instance variable is either a class
- name, a surrogate for a class defined by means of a FROM clause,
- or the keyword NEW or CURRENT.
- NEW and CURRENT can only appear in the action portion of a rule, while
- other instance variables can be used in any SQL statement.
+ name, an alias for a class defined by means of a FROM clause,
+ or the keyword NEW or OLD.
+ (NEW and OLD can only appear in the action portion of a rule, while
+ other instance variables can be used in any SQL statement.) The
+ instance name can be omitted if the first field name is unique
+ across all the classes being used in the current query.
<replaceable>composite_field</replaceable>
is a field of of one of the Postgres composite types,
- while successive composite fields address attributes in the
+ while successive composite fields select attributes in the
class(s) to which the composite field evaluates. Lastly,
<replaceable>field</replaceable>
is a normal (base type) field in the class(s) last addressed. If
<replaceable>field</replaceable>
- is of type <literal>array</literal>,
- then the optional <replaceable>number</replaceable>
- designator indicates a specific element in the array. If no number is
- indicated, then all array elements are returned.
+ is of an array type,
+ then the optional <replaceable>subscript</replaceable>
+ selects a specific element in the array. If no subscript is
+ provided, then the whole array is selected.
</para>
</sect2>
</sect1>
<title>Operators</title>
<para>
- Any built-in system, or user-defined operator may be used in SQL.
- For the list of built-in and system operators consult
- <xref linkend="functions">.
+ Any built-in or user-defined operator may be used in SQL.
+ For the list of built-in operators consult <xref linkend="functions">.
For a list of user-defined operators consult your system administrator
or run a query on the <literal>pg_operator</literal> class.
Parentheses may be used for arbitrary grouping of operators in expressions.
An expression is one of the following:
<simplelist>
- <member>( a_expr )</member>
<member>constant</member>
- <member>attribute</member>
- <member><replaceable>a_expr</replaceable> <replaceable>binary_operator</replaceable> <replaceable>a_expr</replaceable></member>
- <member><replaceable>a_expr</replaceable> <replaceable>right_unary_operator</replaceable></member>
- <member><replaceable>left_unary_operator</replaceable> <replaceable>a_expr</replaceable></member>
+ <member>column</member>
+ <member><replaceable>expression</replaceable> <replaceable>binary_operator</replaceable> <replaceable>expression</replaceable></member>
+ <member><replaceable>expression</replaceable> <replaceable>right_unary_operator</replaceable></member>
+ <member><replaceable>left_unary_operator</replaceable> <replaceable>expression</replaceable></member>
+ <member>( <replaceable>expression</replaceable> )</member>
<member>parameter</member>
<member>functional expression</member>
<member>aggregate expression</member>
</para>
<para>
- We have already discussed constants and attributes. The three kinds of
+ We have already discussed constants and columns. The three kinds of
operator expressions indicate respectively binary (infix), right-unary
(suffix) and left-unary (prefix) operators. The following sections
discuss the remaining options.
<para>
A <firstterm>parameter</firstterm>
is used to indicate a parameter in a SQL function. Typically this
- is used in SQL function definition statement. The form of a
+ is used in SQL function definition statements. The form of a
parameter is:
<synopsis>
<programlisting>
CREATE FUNCTION dept (name)
RETURNS dept
- AS 'select * from
- dept where name=$1'
+ AS 'select * from dept where name = $1'
LANGUAGE 'sql';
</programlisting>
</para>
enclosed in parentheses:
<synopsis>
-<replaceable>function</replaceable> (<replaceable>a_expr</replaceable> [, <replaceable>a_expr</replaceable> ... ] )
+<replaceable>function</replaceable> (<replaceable>expression</replaceable> [, <replaceable>expression</replaceable> ... ] )
</synopsis>
</para>
of which must be of the form:
<synopsis>
-<replaceable>a_expr</replaceable> [ AS <replaceable>result_attname</replaceable> ]
+<replaceable>expression</replaceable> [ AS <replaceable>result_attname</replaceable> ]
</synopsis>
where <replaceable>result_attname</replaceable>
is the name to be assigned to the created column. If
<replaceable>result_attname</replaceable>
is not present, then <productname>Postgres</productname> selects a
- default name based on the contents of <replaceable>a_expr</replaceable>.
- If <replaceable>a_expr</replaceable> is a simple attribute reference
+ default name based on the contents of <replaceable>expression</replaceable>.
+ If <replaceable>expression</replaceable> is a simple attribute reference
then the default name will be the same as that attribute's name, but
otherwise the implementation is free to assign any default name.
</para>
<member>OR</member>
</simplelist>
- A clause is an <replaceable>a_expr</replaceable>
+ A clause is an <replaceable>expression</replaceable>
that evaluates to a <literal>boolean</literal> over a set of instances.
</para>
</sect2>
<para>
The <firstterm>from list</firstterm>
- is a comma-separated list of <firstterm>from expressions</firstterm>.
- Each "from expression" is of the form:
+ is a comma-separated list of <firstterm>from-expressions</firstterm>.
+ The simplest possibility for a from-expression is:
+
+ <synopsis>
+<replaceable>class_reference</replaceable> [ [ AS ] <replaceable class="PARAMETER">alias</replaceable> ]
+ </synopsis>
+
+ where <replaceable>class_reference</replaceable> is of the form
<synopsis>
-[ <replaceable>class_reference</replaceable> ] <replaceable>instance_variable</replaceable>
- {, [ <replaceable>class_ref</replaceable> ] <replaceable>instance_variable</replaceable>... }
+[ ONLY ] <replaceable class="PARAMETER">table_name</replaceable> [ * ]
</synopsis>
- where <replaceable>class_reference</replaceable>
- is of the form
+ The from-expression defines an instance variable that ranges over the
+ rows of the specified table. The instance variable's name is either
+ the table name, or the <replaceable>alias</replaceable> if one is given.
+ Ordinarily, if the table has child tables then the instance variable
+ will range over all rows in the inheritance hierarchy starting with
+ the specified table. If <literal>ONLY</literal> is specified then
+ child tables are not included. A trailing asterisk <literal>*</literal>
+ can be written to specifically indicate that child tables are included
+ (<literal>ONLY</literal> and <literal>*</literal> are mutually
+ exclusive).
+ </para>
+
+ <para>
+ A from-expression can also be a sub-query:
+
+ <synopsis>
+( <replaceable class="PARAMETER">select-statement</replaceable> ) [ AS ] <replaceable class="PARAMETER">alias</replaceable>
+ </synopsis>
+
+ Here, the effect is as though the SELECT were executed and its results
+ stored in a temporary table, which then becomes available as an instance
+ variable under the given <replaceable>alias</replaceable>.
+ </para>
+
+ <para>
+ Finally, a from-expression can be built up from simpler from-expressions
+ using JOIN clauses:
<synopsis>
-<replaceable>class_name</replaceable> [ * ]
+<replaceable class="PARAMETER">from_expression</replaceable> [ NATURAL ] <replaceable class="PARAMETER">join_type</replaceable> <replaceable class="PARAMETER">from_expression</replaceable>
+ [ ON <replaceable class="PARAMETER">join_condition</replaceable> | USING ( <replaceable class="PARAMETER">join_column_list</replaceable> ) ]
</synopsis>
- The "from expression"
- defines one or more instance variables to range over the class
- indicated in <replaceable>class_reference</replaceable>.
- One can also request
- the instance variable to range over only the specific class
- and not those that are beneath the
- indicated class in the inheritance hierarchy by specifying ONLY before
- before the classname.
+ This syntax allows specification of <firstterm>outer joins</firstterm>.
+ For details see the reference page for SELECT.
</para>
</sect2>
left-associative. This may lead to non-intuitive behavior; for
example the boolean operators "<" and ">" have a different
precedence than the boolean operators "<=" and ">=". Also,
- you will sometimes need to add parenthesis when using combinations
+ you will sometimes need to add parentheses when using combinations
of binary and unary operators. For instance
<programlisting>
SELECT 5 & ~ 6;
<para>
Note that the operator precedence rules also apply to user-defined
- operators that <quote>look like</quote> the built-in operators
- with special treatment. For example, if you define a
+ operators that have the same names as the built-in operators
+ mentioned above. For example, if you define a
<quote>+</quote> operator for some custom data type it will have
the same precedence as the built-in <quote>+</quote> operator, no
matter what yours does.
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