MySQL錯誤1066不是唯一的表/別名

Question

的代碼如下：

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

我得到一個「不是唯一表」庫存和我不明白爲什麼。另外，爲什麼庫存和分支？

Answer 1

添加WHERE條款：

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