Posted By: medved (A~z na v~eky Mikov~ce.) on 'CZdatabases'
Title:     Re: zajimavost
Date:      Thu Sep  5 12:08:03 2002

> select count(*) from B where id in (select distinct id from A)
> 
> Takhle bych to delal ja - pro MS SQL
> 
> >   SELECT COUNT(DISTINCT b.id) FROM a,b WHERE a.id = b.id
> > 
> > a to vrati 2 :-)  Je to Informix specific, nebo to funguje i jinde?

Oboji je spravne. Dopad to ale muze mit na vykonnost. Pokud nejsou dobre 
udelane indexy (nebo to databaze neumi), tak se musi pouzit docasna tabulka a 
tam zalezi na jeji velikosti.

Neboli zda je mensi "distinct id from A" nebo "A.id=B.id" mnozina radek. 

> > Jovo.
>                                                                       Libb

Bye

Medved

No matter where you go, everyone is connected.