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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/src/sgml/xfunc.sgml | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml index 55a99c0ff34..537ee6fa254 100644 --- a/doc/src/sgml/xfunc.sgml +++ b/doc/src/sgml/xfunc.sgml @@ -4160,6 +4160,31 @@ supportfn(internal) returns internal </para> <para> + <literal>SupportRequestSimplify</literal> is not used + for <link linkend="queries-tablefunctions">set-returning + functions</link>. Instead, support functions can implement + the <literal>SupportRequestInlineInFrom</literal> request to expand + function calls appearing in the <literal>FROM</literal> clause of a + query. (It's also allowed to support this request for + non-set-returning functions, although + typically <literal>SupportRequestSimplify</literal> would serve as + well.) For this request type, a successful result must be + a <literal>SELECT</literal> Query tree, which will replace + the <literal>FROM</literal> item as though a sub-select had been + written instead. The Query tree must appear as it would after parse + analysis and rewrite processing. One way to ensure that that's true + is to build a SQL string then feed it + through <function>pg_parse_query</function> + and <function>pg_analyze_and_rewrite</function>, or related + functions. <literal>PARAM_EXTERN</literal> <structname>Param</structname> + nodes can appear within the Query to represent the function's + arguments; they will be replaced by the actual argument expressions. + As with <literal>SupportRequestSimplify</literal>, it is the support + function's responsibility that the replacement Query be equivalent to + normal execution of the target function. + </para> + + <para> For target functions that return <type>boolean</type>, it is often useful to estimate the fraction of rows that will be selected by a <literal>WHERE</literal> clause using that function. This can be done by a support function that implements |