postgres.git / summary / log / commit / refs

commit    386e64ea5abf346d887c21ea8869317838ba19b5
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Fri Apr 30 19:10:06 2021 +0000
First released in: 14.0, 9.6.22, 10.17, 11.12, 12.7, 13.3

    Doc: update libpq's documentation for PQfn().
    
    Mention specifically that you can't call aggregates, window functions,
    or procedures this way (the inability to call SRFs was already
    mentioned).
    
    Also, the claim that PQfn doesn't support NULL arguments or results
    has been a lie since we invented protocol 3.0.  Not sure why this
    text was never updated for that, but do it now.
    
    Discussion: https://postgr.es/m/2039442.1615317309@sss.pgh.pa.us


 doc/src/sgml/libpq.sgml | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 174a6b7f37b..875950b83c0 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -5760,15 +5760,32 @@ typedef struct
 
   <para>
    <function>PQfn</function> always returns a valid
-   <structname>PGresult</structname> pointer. The result status should be
+   <structname>PGresult</structname> pointer, with
+   status <literal>PGRES_COMMAND_OK</literal> for success
+   or <literal>PGRES_FATAL_ERROR</literal> if some problem was encountered.
+   The result status should be
    checked before the result is used.   The caller is responsible for
    freeing  the  <structname>PGresult</structname>  with
    <xref linkend="libpq-PQclear"/> when it is no longer needed.
   </para>
 
   <para>
-   Note that it is not possible to handle null arguments, null results,
-   nor set-valued results when using this interface.
+   To pass a NULL argument to the function, set
+   the <parameter>len</parameter> field of that parameter structure
+   to <literal>-1</literal>; the <parameter>isint</parameter>
+   and <parameter>u</parameter> fields are then irrelevant.
+  </para>
+
+  <para>
+   If the function returns NULL, <parameter>*result_len</parameter> is set
+   to <literal>-1</literal>, and <parameter>*result_buf</parameter> is not
+   modified.
+  </para>
+
+  <para>
+   Note that it is not possible to handle set-valued results when using
+   this interface.  Also, the function must be a plain function, not an
+   aggregate, window function, or procedure.
   </para>
 
  </sect1>


[parent: 2efcd502e56a]