Mysql错误1066不唯一的表/别名

Question

代码如下:

Select Branch.BranchName, Sum(Inventory.OnHand) From Inventory, Branch 
Inventory.BranchNum = Branch.BranchNum 
Group By BranchName;

我收到一个“非唯一表”的库存信息，但我不明白为什么。另外，为什么是库存而不是分支？

Answer 1

添加 WHERE 子句:

Select Branch.BranchName, Sum(Inventory.OnHand) 
From Inventory, Branch 
WHERE Inventory.BranchNum = Branch.BranchNum 
Group By BranchName;