如何优化如下SQL语句?
如何优化如下SQL语句呢
当数据达到上万条后，动不动就五十多秒啊
SELECT   ProductName   ,   Total=(SELECT     sum(ProductNumber)   FROM   ProductInfo   WHERE   PID <TBL.PID)+   ProductNumber   FROM     ProductInfo   TBL


------解决方案--------------------
SELECT TBL.ProductName , Total=sum(b.ProductNumber)+TBL.ProductNumber FROM ProductInfo TBL,ProductInfo as b WHERE b.PID <TBL.PID group by TBL.ProductName ,TBL.ProductNumber