Question

我有一大堆表：

Table1: PersonID, A1, A2, A3, ...

Table2: PersonID, B1, B2, B3, ...

Table3: PersonID, C1, C2, C3, ...

Table4: PersonID, D1, D2, D3, ...

...

Table1很特别，因为它实际上包含所有个人（姓名和个人信息），但所有其他表几乎肯定都缺少行（一个人根本没有参与该事件）。

我想要做的是将所有表连接在一起（通过公共PersonID），这样任何缺少的属性都将被留空。所以，当然，我想使用外连接。这就是我试过的：

SELECT * 

FROM Table1, Table2, Table3, Table4, Table5, Table6

LEFT OUTER JOIN Table2 ON Table1.PersonID = Table2.PersonID
LEFT OUTER JOIN Table3 ON Table1.PersonID = Table3.PersonID
LEFT OUTER JOIN Table4 ON Table1.PersonID = Table4.PersonID
LEFT OUTER JOIN Table5 ON Table1.PersonID = Table5.PersonID
LEFT OUTER JOIN Table6 ON Table1.PersonID = Table6.PersonID

这一切都给了我一个内存过载。我想我以某种方式拿走了我所有桌子的笛卡尔积，这让一切都变得窒息。有没有办法做到这一点？

提前致谢！

Answer 1

使用此：

SELECT * 
FROM Table1
LEFT OUTER JOIN Table2 ON Table1.PersonID = Table2.PersonID
LEFT OUTER JOIN Table3 ON Table1.PersonID = Table3.PersonID
LEFT OUTER JOIN Table4 ON Table1.PersonID = Table4.PersonID
LEFT OUTER JOIN Table5 ON Table1.PersonID = Table5.PersonID
LEFT OUTER JOIN Table6 ON Table1.PersonID = Table6.PersonID

查看 SQL Joins 表格了解详情。

Answer 2

改变这个：

SELECT * 

FROM Table1, Table2, Table3, Table4, Table5, Table6

LEFT OUTER JOIN Table2 ON Table1.PersonID = Table2.PersonID
LEFT OUTER JOIN Table3 ON Table1.PersonID = Table3.PersonID
LEFT OUTER JOIN Table4 ON Table1.PersonID = Table4.PersonID
LEFT OUTER JOIN Table5 ON Table1.PersonID = Table5.PersonID
LEFT OUTER JOIN Table6 ON Table1.PersonID = Table6.PersonID

到此：

SELECT * 

FROM Table1
LEFT OUTER JOIN Table2 ON Table1.PersonID = Table2.PersonID
LEFT OUTER JOIN Table3 ON Table1.PersonID = Table3.PersonID
LEFT OUTER JOIN Table4 ON Table1.PersonID = Table4.PersonID
LEFT OUTER JOIN Table5 ON Table1.PersonID = Table5.PersonID
LEFT OUTER JOIN Table6 ON Table1.PersonID = Table6.PersonID

是的，你们拿着所有桌子的笛卡尔积，然后把它加到其他桌子上

多个左连接到单个表

2 个答案: