Обсуждение: Optimize the query, help me please.
Query is:
SELECT * FROM a UNION SELECT * FROM b ORDER BY time DESC LIMIT 100
how can i get only last 100 row from a and b and then do union. Explain of select said that all recond selected from a and b.
thanks.
On 23/11/2011 10:56, Капралов Александр wrote: > Query is: > SELECT * FROM a UNION SELECT * FROM b ORDER BY time DESC LIMIT 100 > > how can i get only last 100 row from a and b and then do union. Explain > of select said that all recond selected from a and b. (select * from a order by time desc limit 100) union (select * from b order by time desc limit 100) order by time desc limit 100; BTW "time" is a reserved word AFAIK, so you should enclose it in double-quotes or call the column something else. Ray. -- Raymond O'Donnell :: Galway :: Ireland rod@iol.ie
Hi,
--
==============================
If Pac-Man had affected us as kids, we'd all be running around in a darkened room munching pills and listening to repetitive music.
(SELECT * FROM a limit 10) union (SELECT * FROM b limit 10)
is what you need
Bèrto
2011/11/23 Капралов Александр <alnkapa@gmail.com>
Query is:SELECT * FROM a UNION SELECT * FROM b ORDER BY time DESC LIMIT 100how can i get only last 100 row from a and b and then do union. Explain of select said that all recond selected from a and b.thanks.
==============================
If Pac-Man had affected us as kids, we'd all be running around in a darkened room munching pills and listening to repetitive music.
Στις Wednesday 23 November 2011 12:56:23 ο/η Капралов Александр έγραψε: > Query is: > SELECT * FROM a UNION SELECT * FROM b ORDER BY time DESC LIMIT 100 > > how can i get only last 100 row from a and b and then do union. Explain of > select said that all recond selected from a and b. > In order to get 100 last rows from a and 100 last rows from b do: (SELECT * FROM a ORDER BY time LIMIT 100) UNION ALL (SELECT * FROM b ORDER BY time LIMIT 100); omitting the "ALL" modifier, you may end up with less rows, since UNION normally returns only distinct rows. > thanks. > -- Achilleas Mantzios