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继续请教mysql查询语句:多表联合查询,如何限定右侧的表如果有对应记录则加入特定的where限制或者limit限制,反之则不加限制
继续请教mysql查询语句:多表联合查询,如何限定右侧的表如果有对应记录则加入特定的where限制或者limit限制,反之则不加限制
如题
6表联合查询,目前用的还是a left join b left join c left join d left join e left join f这样的
为了保证 a表中的每一条记录 在bcedf表中最多只找到一条对应 要加一些条件
但是加了诸如where f.aaa in ( 0 ,1 ,2 ,3)这样的限制后, 查询的结果 全部是 有f表中有对应记录的
希望能把f表中没有对应记录的也查出来 该怎么修改语句呢?
另外在问另一个问题 假设就算加了这样的条件,becdf表中还是有多条,能否在这一条sql语句中限定比如f表只查最新的一条,以防止a表记录在结果中重复出现
回复讨论(解决方案)
一个结果需要通过6各表连接查询，应该说是你的表设计有问题
可先按关联键形成几个过渡表，以减少表间的影响
6表查询，这个生成多大的笛卡尔积啊，反正我是卡死了
因为要生成实时的报表... 所以涉及的业务比较多...
当然,这肯定是前期设计有问题 只是现在没办法推倒重做
1、我上面已经讲了，查询时先产生过渡表，再对过渡表查询
2、通过视图将原来不合理的设计变成合理的设计，查询对视图进行
已解决 加了 f.id is null
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