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Support a COLLATE clause in plpgsql variable declarations.

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This allows the usual rules for assigning a collation to a local variable
to be overridden.  Per discussion, it seems appropriate to support this
rather than forcing all local variables to have the argument-derived
collation.
This commit is contained in:
Tom Lane
2011-04-17 14:54:19 -04:00
parent 88dc6fa7a1
commit c947325856
5 changed files with 136 additions and 12 deletions
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32
doc/src/sgml/plpgsql.sgml
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@ -328,15 +328,17 @@ arow RECORD;
<para>
The general syntax of a variable declaration is:
<synopsis>
<replaceable>name</replaceable> <optional> CONSTANT </optional> <replaceable>type</replaceable> <optional> NOT NULL </optional> <optional> { DEFAULT | := } <replaceable>expression</replaceable> </optional>;
<replaceable>name</replaceable> <optional> CONSTANT </optional> <replaceable>type</replaceable> <optional> COLLATE <replaceable>collation_name</replaceable> </optional> <optional> NOT NULL </optional> <optional> { DEFAULT | := } <replaceable>expression</replaceable> </optional>;
</synopsis>
The <literal>DEFAULT</> clause, if given, specifies the initial value assigned
to the variable when the block is entered. If the <literal>DEFAULT</> clause
is not given then the variable is initialized to the
<acronym>SQL</acronym> null value.
The <literal>CONSTANT</> option prevents the variable from being
assigned to, so that its value will remain constant for the duration of
the block.
assigned to after initialization, so that its value will remain constant
for the duration of the block.
The <literal>COLLATE</> option specifies a collation to use for the
variable (see <xref linkend="plpgsql-declaration-collation">).
If <literal>NOT NULL</>
is specified, an assignment of a null value results in a run-time
error. All variables declared as <literal>NOT NULL</>
@ -768,9 +770,23 @@ $$ LANGUAGE plpgsql;
</para>
<para>
Explicit <literal>COLLATE</> clauses can be written inside a function
if it is desired to force a particular collation to be used regardless
of what the function is called with. For example,
A local variable of a collatable data type can have a different collation
associated with it by including the <literal>COLLATE</> option in its
declaration, for example
<programlisting>
DECLARE
local_a text COLLATE "en_US";
</programlisting>
This option overrides the collation that would otherwise be
given to the variable according to the rules above.
</para>
<para>
Also, of course explicit <literal>COLLATE</> clauses can be written inside
a function if it is desired to force a particular collation to be used in
a particular operation. For example,
<programlisting>
CREATE FUNCTION less_than_c(a text, b text) RETURNS boolean AS $$
@ -779,6 +795,10 @@ BEGIN
END;
$$ LANGUAGE plpgsql;
</programlisting>
This overrides the collations associated with the table columns,
parameters, or local variables used in the expression, just as would
happen in a plain SQL command.
</para>
</sect2>
</sect1>