SQL多个连接

Question

我有4张桌子（如图所示），我想选择发票，发出发票的客户，以及发票的所有项目。

我无法弄清楚怎么样？我应该如何应用联接，还是应该使用子查询？

请帮助我，我真的很震惊。

先谢谢。

Answer 1

简单INNER JOIN应该有效

SELECT I.ItemID,
       C.ClientID,
       IV.InvoiceID
FROM   Items I
       INNER JOIN InvoiceItems II
               ON I.ItemID = II.ItemID
       INNER JOIN Invoice IV
               ON IV.InvoiceID = II.InvoiceID
       INNER JOIN Client C
               ON C.ClientID = IV.ClientID 

Answer 2

Select c.ClientID, i.Invoiceid, it.itemId 
from Clients c
Inner Join Invoice i ON i.ClientId = c.ClientId
Inner Join InvoiceItems ii on ii.InvoiceId = i.InvoiceId
Inner Join Items it on ii.ItemId = it.ItemI
Order by c.Clientid, i.Invoiceid, it.itemId

可以根据需要添加其他列。

Answer 3

问题是什么？这是一个简单的连接

Select * From InvoiceItems ii
Join Items i on ii.ItemID = i.ItemID
Join Invoice inv on ii.InvoceID = inv.InvoiceID
Join Clients c on inv.ClientID = c.ClientID