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>PostgreSQL 8.2.14 Documentation</TH
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>Chapter 37. <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> - <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> Procedural Language</TD
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><A
NAME="PLPGSQL-STRUCTURE"
>37.3. Structure of <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
></A
></H1
><P
> <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> is a block-structured language.
The complete text of a function definition must be a
<I
CLASS="FIRSTTERM"
>block</I
>. A block is defined as:
</P><PRE
CLASS="SYNOPSIS"
>[<SPAN
CLASS="OPTIONAL"
> <<<TT
CLASS="REPLACEABLE"
><I
>label</I
></TT
>>> </SPAN
>]
[<SPAN
CLASS="OPTIONAL"
> DECLARE
<TT
CLASS="REPLACEABLE"
><I
>declarations</I
></TT
> </SPAN
>]
BEGIN
<TT
CLASS="REPLACEABLE"
><I
>statements</I
></TT
>
END [<SPAN
CLASS="OPTIONAL"
> <TT
CLASS="REPLACEABLE"
><I
>label</I
></TT
> </SPAN
>];</PRE
><P>
</P
><P
> Each declaration and each statement within a block is terminated
by a semicolon. A block that appears within another block must
have a semicolon after <TT
CLASS="LITERAL"
>END</TT
>, as shown above;
however the final <TT
CLASS="LITERAL"
>END</TT
> that
concludes a function body does not require a semicolon.
</P
><P
> All key words and identifiers can be written in mixed upper and
lower case. Identifiers are implicitly converted to lowercase
unless double-quoted.
</P
><P
> There are two types of comments in <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
>. A double
dash (<TT
CLASS="LITERAL"
>--</TT
>) starts a comment that extends to the end of
the line. A <TT
CLASS="LITERAL"
>/*</TT
> starts a block comment that extends to
the next occurrence of <TT
CLASS="LITERAL"
>*/</TT
>. Block comments cannot be
nested, but double dash comments can be enclosed into a block comment and
a double dash can hide the block comment delimiters <TT
CLASS="LITERAL"
>/*</TT
>
and <TT
CLASS="LITERAL"
>*/</TT
>.
</P
><P
> Any statement in the statement section of a block
can be a <I
CLASS="FIRSTTERM"
>subblock</I
>. Subblocks can be used for
logical grouping or to localize variables to a small group
of statements.
</P
><P
> The variables declared in the declarations section preceding a
block are initialized to their default values every time the
block is entered, not only once per function call. For example:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION somefunc() RETURNS integer AS $$
DECLARE
quantity integer := 30;
BEGIN
RAISE NOTICE 'Quantity here is %', quantity; -- Quantity here is 30
quantity := 50;
--
-- Create a subblock
--
DECLARE
quantity integer := 80;
BEGIN
RAISE NOTICE 'Quantity here is %', quantity; -- Quantity here is 80
END;
RAISE NOTICE 'Quantity here is %', quantity; -- Quantity here is 50
RETURN quantity;
END;
$$ LANGUAGE plpgsql;</PRE
><P>
</P
><P
> It is important not to confuse the use of
<TT
CLASS="COMMAND"
>BEGIN</TT
>/<TT
CLASS="COMMAND"
>END</TT
> for grouping statements in
<SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> with the database commands for transaction
control. <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
>'s <TT
CLASS="COMMAND"
>BEGIN</TT
>/<TT
CLASS="COMMAND"
>END</TT
>
are only for grouping; they do not start or end a transaction.
Functions and trigger procedures are always executed within a transaction
established by an outer query — they cannot start or commit that
transaction, since there would be no context for them to execute in.
However, a block containing an <TT
CLASS="LITERAL"
>EXCEPTION</TT
> clause effectively
forms a subtransaction that can be rolled back without affecting the
outer transaction. For more about that see <A
HREF="plpgsql-control-structures.html#PLPGSQL-ERROR-TRAPPING"
>Section 37.7.5</A
>.
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distrib
>
Mandriva
>
2010.0
>
i586
>
media
>
contrib-release
>
by-pkgid
>
a866202fe868538f89a755dbcabc378b
>
files
>
357
