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Re: MYISAM INDEX KEY Question
Posted by: Rick James
Date: May 28, 2014 12:48AM

> May I know the reasons that the query does not get 'index_key1' as indexing purpose?

There are many possible reasons. However your two SELECTs are identical.

Another tip... Don't use "SELECT *" if you don't need _all_ the columns. One thing the optimizer will do is pick an index based on what columns it will need. "*" includes `description`, which is not in any INDEX. This limits what optimizations it can do. To see what I mean, try these:

EXPLAIN SELECT client_id, user_id
FROM `users`
WHERE `client_id` LIKE 'nanako' AND `user_id` LIKE ‘jasmine' ;

EXPLAIN SELECT client_id, user_id, password
FROM `users`
WHERE `client_id` LIKE 'nanako' AND `user_id` LIKE ‘jasmine' ;

EXPLAIN SELECT client_id, user_id, description
FROM `users`
WHERE `client_id` LIKE 'nanako' AND `user_id` LIKE ‘jasmine' ;

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