Re: RE: the opposite of a join?

I agree with this. Never use a subquery when a join will work. The optimizer with thank you with performance. James Ausmus wrote:

On 10/3/07, jd.pillion@gmail.com <jd.pillion@gmail.com> wrote:

Hi J, Checkout this, SELECT * FROM tbl_company where id not in (SELECT companyID from tbl_contacts)

Brilliant! This is exactly what I was looking for, and is quite logical/readable! Thanks to everyone for the ideas! J

No, don't do this! It is a very inefficient way to retrieve the information you are looking for (Use a query analysis tool to check it out yourself, if you want) - if your tables get to any larger size at all, it will start having a noticeable performance impact on your script (not to mention your DB) - let the DB do the hard work and use a LEFT JOIN syntax, the database can optimize that much more efficiently. Only if your DB doesn't support the LEFT JOIN syntax would you want to do the above. -James

Regards, Lasitha Alawatta Application Developer Destinations of the World Holding Establishment P O Box: 19950 Dubai, United Arab Emirates ( Ph +971 4 295 8510 (Board) / 1464 (Ext.) 7 Fax +971 4 295 8910 + lasitha.a@dotw.com -----Original Message----- From: John Pillion [mailto:john@conv-dg.com] <mailto:john@conv-dg.com%5D>

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jd.pillion@gmail.com Sent: Wednesday, October 03, 2007 2:21 PM To: php-general@lists.php.net; php-db@lists.php.net Subject: [PHP-DB] the opposite of a join? I have a company table and a contacts table. In the contacts table, there is a field called "companyID" which is a link to a row in the company table. What is the easiest way to query the company table for all the company rows whose ID is NOT linked to in the contact table? Basically, the opposite of a join? Thanks J DOTW DISCLAIMER: This e-mail and any attachments are strictly confidential and intended for the addressee only. If you are not the named addressee you must not >

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