Question

是否有更简单的方法将父数据连接到多个子左连接数据？

表格结构：

Table1 {id, name, data1, data2, datax}
Table2 {id, table1_id, dataA, dataB, userid}
Table3 {id, table1_id, dataD, userid}
Table4 {id, table1_id, dataE, userid}
TableUsers {userid, username, name, email}

SQL查询：

select Table1.*, Table2.*,Table3.*,Table4.*
from Table1 t1
left outer join Table2 t2 on t2.table1_id = t1.id
left outer join Table3 t3 on t3.table1_id = t1.id
left outer join Table4 t4 on t4.table1_id = t1.id

从这里开始，我想用实际的用户名替换userid字段，每个表都有不同的userid数据，因此使用TableUsers的简单左连接不会起作用，因为它只对表有效等于。

我已经考虑过使用子查询来做这件事，但相信这会非常慢：

select Table1.*,(select TableUser.name from TableUser where Table1.userid = TableUser.userid) as T1Name,
 Table2.*,(select TableUser.name from TableUser where Table2.userid = TableUser.userid) as T2Name,
Table3.*, (select TableUser.name from TableUser where Table3.userid = TableUser.userid) as T3Name,
Table4.*,(select TableUser.name from TableUser where Table1.userid = TableUser.userid) as T4Name
from Table1 t1
left outer join Table2 t2 on t2.table1_id = t1.id
left outer join Table3 t3 on t3.table1_id = t1.id
left outer join Table4 t4 on t4.table1_id = t1.id

重点是从SQL数据库迁移到MongoDB。也许我需要重新考虑整个查询...... 欢呼声，

芯片

Answer 1

执行此操作的“正常”方法是添加其他连接：

select Table1.*, t1name.name, Table2.*, t2name.name, Table3.*, t3name.name,
       Table4.*, t4name.name
from Table1 t1
left outer join Table2 t2 on t2.table1_id = t1.id
left outer join Table3 t3 on t3.table1_id = t1.id
left outer join Table4 t4 on t4.table1_id = t1.id
left outer join TableUser t1name on t1.userid = t1name.userid
left outer join TableUser t2name on t2.userid = t2name.userid
left outer join TableUser t3name on t3.userid = t3name.userid
left outer join TableUser t4name on t4.userid = t4name.userid;

如果你有一个索引TableUser(userid)或TableUser(userid, name)，那么这两种方法的表现应该大致相同。

将父数据连接到多个左连接子数据的简单方法

1 个答案: