SQL Server Update with Inner Join

Question

I have 3 tables (simplified):

 tblOrder(OrderId INT)  
  tblVariety(VarietyId INT,Stock INT)  
  tblOrderItem(OrderId,VarietyId,Quantity INT)

Answer 1

You are doing an update. It will update once.

Edit: to solve, you can add in a subquery that will group your orderitems by orderid and varietyid, with a sum on the amount.