On Mon, Apr 26, 2004 at 05:17:45PM -0500, Boyd E. Hemphill wrote: > I thought I heard at the conference that the optimizer only uses a one > index per table in a query regardless of the number of indexes on the > table. > > Is this true?
Yes. The only exception is in a UNION, but that's best thought of as multiple queries anyway. > Are there any more details regarding the use of indexes I can find > in the documentation? Specifically how the optimizer picks which > index to use? I read through 7.2.4 and several other sections but > no luck. The optimizer looks at the available indexes and attempts to find the one that will require the least amount of work, which usually translates to reading the fewest records to find a match. Have you run your queries thru EXPLAIN to see which keys is considers and which one it chooses? Jeremy -- Jeremy D. Zawodny | Perl, Web, MySQL, Linux Magazine, Yahoo! <[EMAIL PROTECTED]> | http://jeremy.zawodny.com/ [book] High Performance MySQL -- http://highperformancemysql.com/ -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
