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>Chapter 39. <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"
>39.2. Structure of <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
></A
></H1
><P
>   Functions written in <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> are defined
   to the server by executing <A
HREF="sql-createfunction.html"
>CREATE FUNCTION</A
> commands.
   Such a command would normally look like, say,
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION somefunc(integer, text) RETURNS integer
AS '<TT
CLASS="REPLACEABLE"
><I
>function body text</I
></TT
>'
LANGUAGE plpgsql;</PRE
><P>
   The function body is simply a string literal so far as <TT
CLASS="COMMAND"
>CREATE
   FUNCTION</TT
> is concerned.  It is often helpful to use dollar quoting
   (see <A
HREF="sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING"
>Section 4.1.2.4</A
>) to write the function
   body, rather than the normal single quote syntax.  Without dollar quoting,
   any single quotes or backslashes in the function body must be escaped by
   doubling them.  Almost all the examples in this chapter use dollar-quoted
   literals for their function bodies.
  </P
><P
>   <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> is a block-structured language.
   The complete text of a function body must be a
   <I
CLASS="FIRSTTERM"
>block</I
>. A block is defined as:

</P><PRE
CLASS="SYNOPSIS"
>[<SPAN
CLASS="OPTIONAL"
> &lt;&lt;<TT
CLASS="REPLACEABLE"
><I
>label</I
></TT
>&gt;&gt; </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 lower case
     unless double-quoted, just as they are in ordinary SQL commands.
    </P
><P
>     Comments work the same way in <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
> code as in
     ordinary SQL.  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 matching occurrence of
     <TT
CLASS="LITERAL"
>*/</TT
>.  Block comments nest.
    </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 $$
&lt;&lt; outerblock &gt;&gt;
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 39.5.5</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 &mdash; 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 39.6.6</A
>.
    </P
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