test donot read

Frank Brammer wrote:
>
> I aggree, but I must correct one thing. For performance, you should use
> EXISTS instead of IN:
>
> update tablea T set col1=(select col1 from tableb B
> where B.part_num=T.part_num)
> where EXISTS (select 1 from tableb B
> where B.part_num = T.part_num);
>
>
> Gary Assa <gsa_at_panix.com> wrote in article <5pqtv0$36d_at_panix.com>...
> > >I have table A with 5000+ rows and table B with 2200+ rows. They are
> > >keyed on a part number. Table A includes all part numbers, table B only
> > >those that need to be updated. I've tried using an update with an
> > >embedded select using several combinations and approaches. They all
> > >update every row of table A instead of the rows that have a match in
 table
> >
> > A common problem, but here's the solution:
> >
> > update tablea T set col1=(select col1 from tableb
> > where part_num=T.part_num)
> > where part_num in (select part_num from tableb);
> >
> > That last part is the trick. This way, it only updates rows that it finds
 

> > Without it, it tries to match all rows, and when there is no match, it
 will
> > update it with a null.
> >
> >
Received on Tue Jul 08 1997 - 00:00:00 CDT