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;标签:语句,JOIN,PCP,USERID,查询,SYS,USER,mysql,LEFT From: https://www.cnblogs.com/laorenzhenhaoa/p/17146718.html