java - 从不同表中减去两个字段并更新MySQL中前一个字段的值

Question

我有两个表:Item_detail(P_name，Available)和Customer_detail(P_name，Quantity)

现在我想从“可用”字段中减去“数量”字段，然后在“可用”字段中设置减去的值。我写了这段代码，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') ;   

请帮忙!!

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'