Re: performance question

"Uwe Hoell" <hoell_at_nospamaeb.de> wrote in message news:3ba8bbf1$0$232$4d4ebb8e_at_businessnews.de.uu.net...
> Is there a difference in performance for:
>
> select * tableA where exists (select * from tableB where tableA.fk =
> tableB.pk)
>
> select * tableA where exists (select null dummy from tableB where
tableA.fk
> = tableB.pk)
>
> tia
>
>

Yes, the first variant might force the optimizer to read the table, while the second variant, when the table is properly indexed, doesn't read the table.

Regards,

Sybrand Bakker, Senior Oracle DBA Received on Wed Sep 19 2001 - 11:07:37 CDT