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>PostgreSQL 8.3.6 Documentation</TH
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>Chapter 38. <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> - <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> Procedural Language</TD
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><H1
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><A
NAME="PLPGSQL-STRUCTURE"
>38.2. 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
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
> A common mistake is to write a semicolon immediately after
<TT
CLASS="LITERAL"
>BEGIN</TT
>. This is incorrect and will result in a syntax error.
</P
></BLOCKQUOTE
></DIV
><P
> A <TT
CLASS="REPLACEABLE"
><I
>label</I
></TT
> is only needed if you want to
identify the block for use
in an <TT
CLASS="LITERAL"
>EXIT</TT
> statement, or to qualify the names of the
variables declared in the block. If a label is given after
<TT
CLASS="LITERAL"
>END</TT
>, it must match the label at the block's beginning.
</P
><P
> All key words are case-insensitive.
Identifiers are implicitly converted to lowercase
unless double-quoted, just as they are in ordinary SQL commands.
</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. Variables declared in a subblock mask any
similarly-named variables of outer blocks for the duration
of the subblock; but you can access the outer variables anyway
if you qualify their names with their block's label. For example:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION somefunc() RETURNS integer AS $$
<< outerblock >>
DECLARE
quantity integer := 30;
BEGIN
RAISE NOTICE 'Quantity here is %', quantity; -- Prints 30
quantity := 50;
--
-- Create a subblock
--
DECLARE
quantity integer := 80;
BEGIN
RAISE NOTICE 'Quantity here is %', quantity; -- Prints 80
RAISE NOTICE 'Outer quantity here is %', outerblock.quantity; -- Prints 50
END;
RAISE NOTICE 'Quantity here is %', quantity; -- Prints 50
RETURN quantity;
END;
$$ LANGUAGE plpgsql;</PRE
><P>
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> There is actually a hidden <SPAN
CLASS="QUOTE"
>"outer block"</SPAN
> surrounding the body
of any <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> function. This block provides the
declarations of the function's parameters (if any), as well as some
special variables such as <TT
CLASS="LITERAL"
>FOUND</TT
> (see
<A
HREF="plpgsql-statements.html#PLPGSQL-STATEMENTS-DIAGNOSTICS"
>Section 38.5.5</A
>). The outer block is
labeled with the function's name, meaning that parameters and special
variables can be qualified with the function's name.
</P
></BLOCKQUOTE
></DIV
><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 similarly-named SQL 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 38.6.5</A
>.
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