Mysql错误1066不唯一表/别名

Question

代码如下：

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

我为Inventory获得了“不唯一的表”，我不明白为什么。另外，为什么库存而不是分支？

Answer 1

添加WHERE子句：

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