Always check whether all your queries really use the indexes that you have created in the tables. 始终检查您的所有查询是否真正使用您在表中创建的索引。Use the EXPLAIN statement, as described in Section 8.8.1, “Optimizing Queries with EXPLAIN”.使用EXPLAIN语句，如第8.8.1节，“使用EXPLAIN优化查询”所述。