Re: Optimize the query, help me please.

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