Document PERFORM limitation when using WITH queries.

Backpatch to 9.0 and 9.1.

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diff --git a/doc/src/sgml/plpgsql.sgml b/doc/src/sgml/plpgsql.sgml
index 08c3658d5e37171f779e772089b448a76fbec923..a2482de2b95b63653be507219c895d29e62d45d3 100644 (file)
--- a/doc/src/sgml/plpgsql.sgml
+++ b/doc/src/sgml/plpgsql.sgml
@@ -940,6 +940,9 @@ PERFORM query;
      result.  Write the query the same
      way you would write an SQL SELECT command, but replace the
      initial keyword SELECT with PERFORM.
+     For WITH queries, use PERFORM and then
+     place the query in parentheses.  (In this case, the query can only
+     return one row.)
      PL/pgSQL variables will be
      substituted into the query just as for commands that return no result,
      and the plan is cached in the same way.  Also, the special variable