Optimize the query, help me please.

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,

(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 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.

--
==============================
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