From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Kerem Kat <keremkat(at)gmail(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Adding CORRESPONDING to Set Operations |
Date: | 2011-09-24 15:49:33 |
Message-ID: | 8930.1316879373@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Kerem Kat <keremkat(at)gmail(dot)com> writes:
> There is a catch inserting subqueries for corresponding in the planner.
> Parser expects to see equal number of columns in both sides of the
> UNION query. If there is corresponding however we cannot guarantee that.
Well, you certainly need the parse analysis code to be aware of
CORRESPONDING's effects. But I think you can confine the changes to
adjusting the computation of a SetOperationStmt's list of output column
types. It might be a good idea to also add a list of output column
names to SetOperationStmt, and get rid of the logic that digs down into
the child queries when we need to know the output column names.
> Target columns, collations and types for the SetOperationStmt are
> determined in the parser. If we pass the column number equality checks,
> it is not clear that how one would proceed with the targetlist generation
> loop which is a forboth for two table's columns.
Obviously, that logic doesn't work at all for CORRESPONDING, so you'll
need to have a separate code path to deduce the output column list in
that case.
regards, tom lane
From | Date | Subject | |
---|---|---|---|
Next Message | Bruce Momjian | 2011-09-24 16:13:34 | Re: Large C files |
Previous Message | Tom Lane | 2011-09-24 15:41:55 | Re: Large C files |