sql子查询 order by失效问题

Posted 2021-01-25 zhoupan

一、问题描述  三表联合查询  按主表的时间倒叙并分页

　　下面sql语句 ORDER BY失效 ，如果把 ORDER BY  放在最后 比如有20条数据 第一页会是10 -1 第二页是20-11  分页不正确

　　查询资料发现：在mysql5.7中，如果不加limit，系统会把order by优化掉。

 　　在mysql5.7手册的8.2.2.1中有解释：

　　子查询的优化是使用半连接的策略完成的(The optimizer uses semi-join strategies to improve subquery execution)

　　使用半连接进行优化，子查询语句必须满足一些标准(In MySQL, a subquery must satisfy these criteria to be handledas a semi-join)。

　　其中一个标准是:必须不是一个包含了limit和order by的语句(It must not have ORDER BY with LIMIT.)

　　解决方法一：子查询里外都排序   

　　解决方法二：在嵌入一个子查询（好像也是里外都排序）

　　SELECT * FROM (
　　SELECT * FROM (
　　SELECT * FROM zs_safe_confess B WHERE B.ENABLE = 1 ORDER BY B.CREATE_TIME DESC, B.UPDATE_TIME DESC LIMIT 0,10) A
　　LEFT JOIN zs_safe_confess_content C ON A.ID = C.CSAFE_ID)D
　　LEFT JOIN zs_resources ON D.ID = zs_resources.ID AND zs_resources.TYPE = 10 AND zs_resources.ENABLE = 1
　　ORDER BY D.CREATE_TIME DESC, D.UPDATE_TIME DESC

SELECT A.*,
        zs_safe_confess_content.CID,
        zs_safe_confess_content.CSAFE_ID,
        zs_safe_confess_content.CSTATUS,
        zs_safe_confess_content.CCONTENT,
        zs_safe_confess_content.CCHECK_RESULT,
        zs_safe_confess_content.CCREATE_TIME,
        zs_safe_confess_content.CUPDATE_TIME,
        zs_safe_confess_content.CUSER_ID,
        zs_safe_confess_content.CUSER_NAME,
        zs_safe_confess_content.CENABLE,
        zs_safe_confess_content.CBACKUP_01,
        zs_safe_confess_content.CBACKUP_02,
        zs_safe_confess_content.CBACKUP_03,
        zs_resources.RID AS RID,
        zs_resources.ID AS ID,
        zs_resources.TYPE AS RTYPE,
        zs_resources.URL AS RURL,
        zs_resources.RESOURCE_CODE AS RRESOURCE_CODE,
        zs_resources.FILE_NAME AS RFILE_NAME,
        zs_resources.FILE_SIZE AS RFILE_SIZE,
        zs_resources.CREATOR AS RCREATOR,
        zs_resources.CREATETIME AS RCREATETIME,
        zs_resources.MODIFIER AS RMODIFIER,
        zs_resources.UPDATETIME AS RUPDATETIME,
        zs_resources.ENABLE AS RENABLE FROM (
        SELECT
        zs_safe_confess.ID,
        zs_safe_confess.SAFE_NAME, zs_safe_confess.DEPT_NAME,
        zs_safe_confess.DEPT_ID, zs_safe_confess.PROJECT_NAME,
        zs_safe_confess.PROJECT_NUMBER,
        zs_safe_confess.PROJECT_PERSON,
        zs_safe_confess.WORK_ADDRESS, zs_safe_confess.WORK_NUMBER,
        zs_safe_confess.COMPANY_PERSON, zs_safe_confess.COMPANY_PHONE,
        zs_safe_confess.FACTORY_PERSON,
        zs_safe_confess.FACTORY_PHONE,
        zs_safe_confess.DANGER_DISCERN, zs_safe_confess.ENVIRONMENT_DISCREN,
        zs_safe_confess.DANGER_MEASURES,zs_safe_confess.ENVIRONMENT_MEASURES,
        zs_safe_confess.DANGER_MANAGER, zs_safe_confess.MANAGER_TIME,
        zs_safe_confess.SCENE_COMFIRM, zs_safe_confess.SCENE_COMFIRM_TIME,
        zs_safe_confess.COMFIRM_CHECK_PERSON,
        zs_safe_confess.COMFIRM_CHECK_TIME,
        zs_safe_confess.TEST_BEFORE_PERSON, zs_safe_confess.TEST_BEFORE_TIME,
        zs_safe_confess.TEST_PERSON,
        zs_safe_confess.TEST_TIME,
        zs_safe_confess.TEST_AFTER_PERSON,zs_safe_confess.TEST_AFTER_TIME,zs_safe_confess.STATUS,zs_safe_confess.TYPE
        ,zs_safe_confess.CREATE_TIME,zs_safe_confess.UPDATE_TIME,zs_safe_confess.USER_ID,zs_safe_confess.USER_NAME,zs_safe_confess.ENABLE
        ,zs_safe_confess.BACKUP_01,zs_safe_confess.BACKUP_02,zs_safe_confess.BACKUP_03
        FROM zs_safe_confess WHERE zs_safe_confess.ENABLE = 1 ORDER BY CREATE_TIME DESC, UPDATE_TIME DESC LIMIT 0,10) A 
        LEFT JOIN zs_safe_confess_content ON A.ID = zs_safe_confess_content.CSAFE_ID  
        LEFT JOIN zs_resources ON A.ID = zs_resources.ID  AND zs_resources.TYPE = 10 AND zs_resources.ENABLE = 1 (ORDER BY A.CREATE_TIME DESC, A.UPDATE_TIME DESC)(这是解决方法一)