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9.3. where 优化

where 条件的顺序影响查询速度

EXPLAIN select *,from_unixtime(sendtime) from sms where id='461539' and content like '13%';
/* 0 rows affected, 1 rows found. Duration for 1 query: 0.218 sec. */

EXPLAIN select *,from_unixtime(sendtime) from sms where content like '13%' and id='461539';
/* 0 rows affected, 1 rows found. Duration for 1 query: 0.717 sec. */