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From: Josh Berkus <josh@agliodbs.com>
Reply-To: josh@agliodbs.com
Organization: Aglio Database Solutions
To: Richard Huxton <dev@archonet.com>, pgsql-sql@postgresql.org
Subject: Re: UPDATE ... FROM vs standard SQL
Date: Fri, 7 Jun 2002 11:50:55 -0700
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Richard,

> Tell me about it. Where I'm using MySQL on client web-servers I find myse=
lf=20
> porting the data into PG to massage it then putting the results back into=
=20
> MySQL. One of the things missing from the various reviews/comparisons on =
the=20
> web is any actual comparison of usage for DBA tasks (as opposed to handli=
ng=20
a=20
> message-board app etc)

But MySQL does handle message-baord apps very well.  If only MySQL AB and=
=20
NuSphere would stick to that and not try to poach in transactional database=
=20
space ...

> Nope - mostly work with PG/MySQL/MS-SQL/Access. I use all the features at=
=20
the=20
> psql prompt, but like to stick to the standard for app-generated queries.

Well, this will work on any database with *full* SQL92 support:

UPDATE tablea SET field3 =3D (SELECT field5
						FROM tableb
						WHERE tableb.field2 =3D tablea.field1);

... and won't be as slow as an IN query.  Quite.

However, MS SQL 7.0 does not support correlated subqueries outside of the=
=20
WHERE clause (I'm not sure about SQL 2000).   For MS Access, well, forget=
=20
using subqueries at all unless you have all day ...

And for MySQL, you're hosed.   Tell your clients they need a different=20
database.

--=20
-Josh Berkus

______AGLIO DATABASE SOLUTIONS___________________________
                                        Josh Berkus
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