Re: Execution order of CTEs / set_config and current_setting in the same query

Tom Lane:
> I think you're on fairly shaky ground here.  Generally speaking, a CTE
> will be executed/read only when the parent query needs the next row from
> it.  Your examples ensure that the CTE is read before the parent query's
> results are computed; but in realistic usage you'd presumably be joining
> the CTE with some other table(s), and then the execution order is going
> to be a lot harder to predict.  This approach is also going to
> fundamentally not work for settings that need to apply during planning
> of the query (which, notably, probably includes "role").

Ok, thanks for confirming that.

> You'd be far better off to investigate ways to send SET LOCAL first,
> without incurring a separate network round trip for that.  If you're
> using simple query mode that's easy, you can just do
> 
>     res = PQexec("SET LOCAL ... ; <real query>");
> 
> In extended query mode you can't get away with that, but you might be able
> to issue the SET LOCAL without immediately waiting for the result.

Yes, that's what we did so far. We switched to set_config to parametrize 
the query.

Is there any way to not wait for a SELECT? I don't care about the 
resultset, so I need something like PERFORM but for SQL, not plpgsql, I 
think?