请问我这条sql应该怎样改?

Question

这是一条求库存小于0的商品，但出错提示：stock不存在SELECT     pdid, SUM(iQty) - SUM(oQty) AS stock
FROM         table
WHERE     (stock < 0)
GROUP BY pdid

Answer 1

SELECT    pdid, SUM(iQty) - SUM(oQty) AS stock 
FROM        table 
GROUP BY pdid
having ( SUM(iQty) - SUM(oQty))<0

Answer 2

SELECT 
   pdid, SUM(iQty) - SUM(oQty) AS stock 
FROM     
   table 
GROUP BY
   pdid 
having ( SUM(iQty) - SUM(oQty)) <0

Answer 3

SELECT 
   pdid, SUM(iQty) - SUM(oQty) AS stock 
FROM     
   table 
GROUP BY
   pdid 
having ( SUM(iQty) - SUM(oQty)) <0

Answer 4

SELECT * FROM (
SELECT    pdid, SUM(iQty) - SUM(oQty) AS stock
FROM        table
WHERE    
GROUP BY pdid) T WHERE (stock < 0)

Answer 5

SELECT    pdid, SUM(iQty - oQty) AS stock
FROM        table
GROUP BY pdid
having SUM(iQty - oQty) < 0