mysql查询语句简单优化

show processlist;
kill ID;    

2. explain 分析查询语句

explain SELECT * FROM CASE_TEST PCP LEFT JOIN SYS_USER SU ON SU.USERID = PCP.UPDATE_PERSON
                                       LEFT JOIN SYS_USER su1 on su1.USERID = PCP.STORAGE_PERSON
                                       LEFT JOIN SYS_USER su2 on su2.USERID = PCP.DELETE_PERSON;
-- type all的key为空的没有用到索引

3. 给关联查询的表 SYS_USER 加索引

4. 继续explain

　结果中key还是为空，但是possible_keys已有值

5. force index

explain SELECT * FROM PWLP_CASE_PUBLIC PCP LEFT JOIN SYS_USER SU force index(`sys_user_USERID_uindex`)ON SU.USERID = PCP.UPDATE_PERSON
                                       LEFT JOIN SYS_USER su1 force index(`sys_user_USERID_uindex`)on su1.USERID = PCP.STORAGE_PERSON
                                       LEFT JOIN SYS_USER su2 force index(`sys_user_USERID_uindex`)on su2.USERID = PCP.DELETE_PERSON;