Substacting從不同的表中的兩個領域，在MySQL

Question

更新以前的字段中的值我有兩個表：Item_detail（P_name，可用）和Customer_detail（P_name，數量）

現在我想減去「數量」字段從「可用」字段中選擇，然後在「可用」字段中設置相減的值。我寫這段代碼但它不起作用

update Item_detail 
    set Available=(
     select (A.Available-B.Quantity) as Available 
      from Item_detail as A 
      join (select Quantity from Customer_detail where P_name='ipod') as B 
      where A.P_name='ipod') ; 

請幫忙!!

Answer 1

UPDATE Item_detail JOIN Customer_detail USING (P_name) 
SET Item_detail.Available = Item_detail.Available - Customer_detail.Quantity 
WHERE P_name='ipod' 

Answer 2

希望這將幫助你

UPDATE Item_detail A 
JOIN (SELECT Quantity FROM Customer_detail WHERE P_name='ipod') AS B  
SET Available=A.Available-B.Quantity 
WHERE A.P_name='ipod';