"Steinar H. Gunderson" <[EMAIL PROTECTED]> writes: > On Sat, Dec 11, 2004 at 03:17:13PM +0100, Tomas Skäre wrote: > > select c.* from cjm_object c > > inner join > > (select max(timestamp) as timestamp,objectid,field from cjm_object > > group by objectid,field) t > > using(timestamp,objectid,field) > > where 1=1 and data is not null > > order by objectid,field; > > Usually, SELECT max(field) FROM table is better written in PostgreSQL as > SELECT field FROM table ORDER field DESC LIMIT 1.
Well, my subquery doesn't return just one row, but one for each objectid,field combination in the table. I could rewrite it to something like this: select c.* from cjm_object c where exists (select timestamp from cjm_object t where c.objectid=t.objectid and c.field=t.field order by timestamp desc limit 1) and data is not null order by objectid; But that seems to be even slower, even if it can use an index scan in the subquery. Also it doesn't give the same result set, but I haven't looked into what's wrong yet. > I don't see the point of "where 1=1", though... It's just because the actual query is generated by a program, and it's easier to always have "where 1=1" and then add optional conditions with "and ...". Tomas ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly