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Re: Need recommendation regarding IN expression
Posted by: Jay Pipes
Date: February 23, 2006 10:55AM

Solon Barns wrote:
> Thank you!
>
> I do need GROUP BY because I will be selecting
> time on page per registrant (I made a mistake in
> the first query).

Cool, looks like you got the query correct! :)

> BTW, you specified the s.report_id = 1569 as JOIN
> condition rather than WHERE condition, is it more
> efficient?

For an INNER JOIN, the optimizer is capable of understanding that having the report_id = 1569 is equivalent to filtering the selected_registrants table *before* doing the join to page_views. This is a stylistic thing that I have adopted for two reasons:

1) I believe it makes the SQL more clear in where the filter on report_id is occurring.
2) If you choose to at some point change the INNER JOIN to a LEFT JOIN, you have your filter in the correct place (the ON condition vs. the WHERE clause)

HTH

Jay Pipes
Community Relations Manager, North America, MySQL Inc.

Got Cluster? http://www.mysql.com/cluster
Personal: http://jpipes.com

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Re: Need recommendation regarding IN expression
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