| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Marti Raudsepp <marti(at)juffo(dot)org> |
| Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: UNION ALL with WHERE clause does not use Merge Append |
| Date: | 2012-08-16 14:59:12 |
| Message-ID: | 12520.1345129152@sss.pgh.pa.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Marti Raudsepp <marti(at)juffo(dot)org> writes:
> Is this just a planner shortcoming or a bug? Or is there some
> justification for this behavior?
Per the comment in is_safe_append_member():
* It's only safe to pull up the child if its jointree contains exactly
* one RTE, else the AppendRelInfo data structure breaks. The one base RTE
* could be buried in several levels of FromExpr, however.
*
* Also, the child can't have any WHERE quals because there's no place to
* put them in an appendrel. (This is a bit annoying...)
This will probably get fixed someday, but I wouldn't recommend holding
your breath for it.
regards, tom lane
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Alvaro Herrera | 2012-08-16 15:15:24 | Re: [COMMITTERS] pgsql: Clean up the #include mess a little. |
| Previous Message | Bruce Momjian | 2012-08-16 14:49:03 | Re: pgsql: In docs, change a few cases of "not important" to "unimportant". |