Can someone recommend a good tutorial on MySQL indexes, specifically when used in an order by clause during a join? [closed]

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I could try to post and explain the exact query I'm trying to run, but I'm going by the old adage of, "give a man a fish and he'll eat for a day, teach a man to fish and he'll eat for the rest of his life." SQL optimization seems to be very query-specific, and even if you could solve this one particular query for me, I'm going to开发者_如何学编程 have to write many more queries in the future, and I'd like to be educated on how indexes work in general.

Still, here's a quick description of my current problem. I have a query that joins three tables and runs in 0.2 seconds flat. Awesome. I add an "order by" clause and it runs in 4 minutes and 30 seconds. Sucky. I denormalize one table so there is one fewer join, add indexes everywhere, and now the query runs in... 20 minutes. What the hell? Finally, I don't use a join at all, but rather a subquery with "where id in (...) order by" and now it runs in 1.5 seconds. Pretty decent. What in God's name is going on? I feel like if I actually understood what indexes were doing I could write some really good SQL.

Anybody know some good tutorials? Thanks!

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I would recommend two books I recently read:

1. High Performance MySQL
2. Refactoring SQL Applications

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Not a very riveting answer, but I've found the official docs to give good background:

http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html

A few things you could try (assuming you've already analysed the optimizer path with EXPLAIN):

• Try running the query with USE INDEX (<your index name here>) to see if your index usage would actually provide the performance you expect.
• Make sure the order of your columns in any composite index reflects the way you expect that index to be used (sorry if that's a bit vague, but MySql index usage can be a bit quirky at times).