manually setting the command tag (was Re: 8.4: suppress_redundant_updates trigger vs. "Upsert" logic)

Mark Reid wrote:

> It'll similarly break any code where a result of "UPDATE 0" is assumed to
> indicate that the record does not exist.

I wonder if this could be helped if the trigger had a way of overriding
the emitted command tag.

There are countless reports of trouble because somebody has an INSTEAD
rule in the table, and the tag emits something that's not quite
acceptable for some outer software layer. The problem is that there's
no way at all to make the command tag behave!

For example, we could offer a new SPI function, say SPI_settag(), which
sets the command tag string. PL/pgSQL could expose this via a new
command, for example COMMANDTAG.

So if there's a function that is used in a INSTEAD rule for (say) an
UPDATE, this function would finish with COMMANDTAG 'UPDATE num' and make
the external framework happy.

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.