当前位置: 首页> 健康> 知识 > 网站网站制作网_哪里能做网站_seo深圳网络推广_推广团队

网站网站制作网_哪里能做网站_seo深圳网络推广_推广团队

时间:2025/7/10 3:12:11来源:https://blog.csdn.net/lipviolet/article/details/143335899 浏览次数:0次
网站网站制作网_哪里能做网站_seo深圳网络推广_推广团队

目录标题

  • join时以大表为基表

join时以大表为基表

  • 查不动

    explain  select u.id as useId, u.open_id as userOpenId, u.name as userName, u.phone as userPhone, s.id as shopId, s.shop_id as shopNum, s.shop_name as shopName from jml_mp_wechatuser u right join jml_shop s on u.id = shopkeeper_id where u.phone = '6D26B768750A90426AAA4CE04FA4CCBB'
    

    在这里插入图片描述

  • 查不动

    EXPLAIN select u.id as useId, u.open_id as userOpenId, u.name as userName, u.phone as userPhone, s.id as shopId, s.shop_id as shopNum, s.shop_name as shopName from jml_shop s LEFT JOIN jml_mp_wechatuser u on u.id = s.shopkeeper_id where u.phone = '6D26B768750A90426AAA4CE04FA4CCBB'
    

    在这里插入图片描述

  • 5s

    EXPLAIN select u.id as useId, u.open_id as userOpenId, u.name as userName, u.phone as userPhone, s.id as shopId, s.shop_id as shopNum, s.shop_name as shopName from jml_shop s LEFT JOIN jml_mp_wechatuser u on u.open_id = s.shopkeeper_openid where u.phone = '6D26B768750A90426AAA4CE04FA4CCBB'
    

    在这里插入图片描述

  • 3s

    explain  select u.id as useId, u.open_id as userOpenId, u.name as userName, u.phone as userPhone, s.id as shopId, s.shop_id as shopNum, s.shop_name as shopName from jml_mp_wechatuser u left join jml_shop s on u.id = shopkeeper_id where u.phone = '6D26B768750A90426AAA4CE04FA4CCBB'
    

    在这里插入图片描述

  • 4s

    explain  select u.id as useId, u.open_id as userOpenId, u.name as userName, u.phone as userPhone, s.id as shopId, s.shop_id as shopNum, s.shop_name as shopName from jml_mp_wechatuser u left join jml_shop s on u.open_id = s.shopkeeper_openid where u.phone = '6D26B768750A90426AAA4CE04FA4CCBB'
    

    在这里插入图片描述

A left join B = B right join A; join的原理是以基准表为底,根据on的条件for循环去另一张表找到等值进而关联。所以显而易见,影响join效率的是等值的长度及for循环次数。以大表为基准可以有效减少for循环次数,选取主键关联可以更快的判断等值。

如何join? on主键+大表为基准!

关键字:网站网站制作网_哪里能做网站_seo深圳网络推广_推广团队

版权声明:

本网仅为发布的内容提供存储空间,不对发表、转载的内容提供任何形式的保证。凡本网注明“来源:XXX网络”的作品,均转载自其它媒体,著作权归作者所有,商业转载请联系作者获得授权,非商业转载请注明出处。

我们尊重并感谢每一位作者,均已注明文章来源和作者。如因作品内容、版权或其它问题,请及时与我们联系,联系邮箱:809451989@qq.com,投稿邮箱:809451989@qq.com

责任编辑: