Tim Harsch writes:
>
>
> Don't think so, the database would clearly have to visit every row in order
> to know there are none that match.
Wrong... at least for Sybase.
In a table with 4 million rows, doing a check on an indexed column:
select 1 from eC_user where exists (select * from eC_user where userId = 999999999)
Table: eC_user scan count 0, logical reads: (regular=0 apf=0 total=0),
physical reads: (regular=0 apf=0 total=0), apf IOs used=0
Table: eC_user scan count 1, logical reads: (regular=3 apf=0 total=3),
physical reads: (regular=0 apf=0 total=0), apf IOs used=0
Total writes for this command: 0
In this case it only needs to do 3 IO operations to find that no rows
match...
Michael
--
Michael Peppler - Data Migrations Inc. - http://www.mbay.net/~mpeppler
[EMAIL PROTECTED] - [EMAIL PROTECTED]
International Sybase User Group - http://www.isug.com
