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Note incompatibility with Oracle's version of FOR ... REVERSE, per

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Andrew Dunstan.  Minor other improvements in documentation of integer
FOR loops.
This commit is contained in:
Tom Lane 2007-07-15 00:45:16 +00:00
parent d849c5d182
commit a69f9028b5
1 changed files with 26 additions and 8 deletions
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34
doc/src/sgml/plpgsql.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.113 2007/07/14 23:02:25 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.114 2007/07/15 00:45:16 tgl Exp $ -->
<chapter id="plpgsql">
<title><application>PL/pgSQL</application> - <acronym>SQL</acronym> Procedural Language</title>
@ -1757,7 +1757,7 @@ END LOOP;
</para>
</sect3>
<sect3>
<sect3 id="plpgsql-integer-for">
<title><literal>FOR</> (integer variant)</title>
<synopsis>
@ -1777,7 +1777,8 @@ END LOOP <optional> <replaceable>label</replaceable> </optional>;
the lower and upper bound of the range are evaluated once when entering
the loop. If the <literal>BY</> clause isn't specified the iteration
step is 1, otherwise it's the value specified in the <literal>BY</>
clause. If <literal>REVERSE</> is specified then the step value is
clause, which again is evaluated once on loop entry.
If <literal>REVERSE</> is specified then the step value is
subtracted, rather than added, after each iteration.
</para>
@ -1785,17 +1786,15 @@ END LOOP <optional> <replaceable>label</replaceable> </optional>;
Some examples of integer <literal>FOR</> loops:
<programlisting>
FOR i IN 1..10 LOOP
-- some computations here
RAISE NOTICE 'i is %', i;
-- i will take on the values 1,2,3,4,5,6,7,8,9,10 within the loop
END LOOP;
FOR i IN REVERSE 10..1 LOOP
-- some computations here
-- i will take on the values 10,9,8,7,6,5,4,3,2,1 within the loop
END LOOP;
FOR i IN REVERSE 10..1 BY 2 LOOP
-- some computations here
RAISE NOTICE 'i is %', i;
-- i will take on the values 10,8,6,4,2 within the loop
END LOOP;
</programlisting>
</para>
@ -1805,6 +1804,13 @@ END LOOP;
in the <literal>REVERSE</> case), the loop body is not
executed at all. No error is raised.
</para>
<para>
If a <replaceable>label</replaceable> is attached to the
<literal>FOR</> loop then the integer loop variable can be
referenced with a qualified name, using that
<replaceable>label</replaceable>.
</para>
</sect3>
</sect2>
@ -3654,6 +3660,18 @@ a_output := a_output || $$ if v_$$ || referrer_keys.kind || $$ like '$$
</para>
</listitem>
<listitem>
<para>
Integer <command>FOR</> loops with <literal>REVERSE</> work
differently: <application>PL/SQL</> counts down from the second
number to the first, while <application>PL/pgSQL</> counts down
from the first number to the second, requiring the loop bounds
to be swapped when porting. This incompatibility is unfortunate
but is unlikely to be changed. (See <xref
linkend="plpgsql-integer-for">.)
</para>
</listitem>
</itemizedlist>
</para>