Re: union vs. sort

Karel Zak <zakkr@zf.jcu.cz> writes:
> On Tue, Apr 06, 2004 at 10:33:25AM -0400, Tom Lane wrote:
>> This isn't simply a matter of "omitting the sort".

>  I didn't  talk about  "Append" result,  but about  "Unique" result. The
>  ORDER BY  in UNION  query works  with final  concanated data  -- that's
>  right. My question is why a result from this ORDER BY is again sorted:

Oh, okay, that's just something that never got done, per this old
comment:

        /*
         * We set current_pathkeys NIL indicating we do not know sort
         * order.  This is correct when the top set operation is UNION
         * ALL, since the appended-together results are unsorted even if
         * the subplans were sorted.  For other set operations we could be
         * smarter --- room for future improvement!
         */

I've committed changes to do the right thing in CVS tip.

			regards, tom lane