Question

我们保持着内容的历史。我们希望获得每个内容的更新条目，创建时间和更新时间应该是内容的第一个条目。该查询包含多个选择以及具有如此多左连接的where子句。数据集非常庞大，因此查询执行时间超过60秒。请帮助改善相同。查询：

select * from (select * from (

    SELECT c.*, initCMS.initcreatetime, initCMS.initupdatetime, user.name as partnerName, r.name as rightsName, r1.name as copyRightsName, a.name as agelimitName, ct.type as contenttypename, cat.name as categoryname, lang.name as languagename FROM ContentCMS c 

        left join ContentCategoryType ct on ct.id = c.contentType 
        left join User user on c.contentPartnerId = user.id 
        left join Category cat on cat.id = c.categoryId 
        left join Language lang on lang.id = c.languageCode 
        left join CopyRights r on c.rights = r.id 
        left join CopyRights r1 on c.copyrights = r1.id 
        left join Age a on c.ageLimit = a.id 
        left outer join (

            SELECT contentId, createTime as initcreatetime, updateTime as initupdatetime from ContentCMS cms where cms.deleted='0'

        ) as initCMS on initCMS.contentId = c.contentId WHERE c.deleted='0' order by c.id  DESC

) as temp group by contentId) as c where c.editedBy='0'

任何帮助都将受到高度赞赏。谢谢。

Answer 1

只是部分评估和建议，因为您的查询似乎没有正确形成

此左连接似乎无用

    FROM ContentCMS c 
    ......
    left join (
        SELECT contentId
            , createTime as initcreatetime
            , updateTime as initupdatetime 
        from ContentCMS cms 
        where cms.deleted='0'
    ) as initCMS on initCMS.contentId = c.contentId

同桌

在连接中的子查询中的顺序（无限制）是无用的，因为连接有序值或无序值会产生相同的结果

groupId的组是奇怪的，因为没有聚合函数而且没有聚合函数的组的sue是不推荐使用的是sql 如果你需要不同的值，或者每个contentId只需要一行，你就应该以非随意的方式使用distinct或者反转这个值（使用group by without aggregation function retrive），并且在mysql的最新版本中是不允许的（通过deafult）非汇总列的随意值。

对于部分eval，您的查询应该重构为

SELECT c.*
          , c.initcreatetime
          , c.initupdatetime
          , user.name as partnerName
          , r.name as rightsName
          , r1.name as copyRightsName
          , a.name as agelimitName
          , ct.type as contenttypename
          , cat.name as categoryname
          , lang.name as languagename 
      FROM ContentCMS c 
      left join ContentCategoryType ct on ct.id = c.contentType 
      left join User user on c.contentPartnerId = user.id 
      left join Category cat on cat.id = c.categoryId 
      left join Language lang on lang.id = c.languageCode 
      left join CopyRights r on c.rights = r.id 
      left join CopyRights r1 on c.copyrights = r1.id 
      WHERE c.deleted='0' 
) as temp

对于其余部分，您应该明确地选择您实际需要为其他人添加适当聚合函数的列

同样，嵌套子查询只是为了不正确地减少行而没有帮助提高性能......你还应该重新评估数据建模和设计。

使用子查询改进MySql查询左外连接

1 个答案: