SELECT DISTINCT TOP (100) PERCENT DATEADD(dd,-1,a.date) as date, a.ItemID_YMC, a.ItemID_YMC2, b.PV
FROM     ABC  AS a LEFT OUTER JOIN
                EFG AS b 
        ON a.ItemID_YMC = b.ItemID_YMC AND a.date = b.date AND b.PV =   --就是这个b.PV这个是什么意思？？？
                    (SELECT   MAX(PV) AS Expr1
                     FROM      dbo.DS04_YMC_BaiDuLiuLiang AS c
                     WHERE   (b.ItemID_YMC = ItemID_YMC) AND (b.date = date)) 

大神好，我有个问题：
我能看懂是LEFT JOIN
也能看懂ON后面 “a.ItemID_YMC = b.ItemID_YMC AND a.date = b.date”
但是到  “ AND b.PV =   
                    (SELECT   MAX(PV) AS Expr1
                     FROM      dbo.DS04_YMC_BaiDuLiuLiang AS c
                     WHERE   (b.ItemID_YMC = ItemID_YMC) AND (b.date = date)) ”
就看不明白了。这里的b.PV 为什么没有 = “一个东西”
例如 a.ItemID_YMC = b.ItemID_YMC 或者  a.date = b.date
求解。。。

等号后面的就是一个“东西”嘛。
 
                   (SELECT   MAX(PV) AS Expr1
                     FROM      dbo.DS04_YMC_BaiDuLiuLiang AS c
                     WHERE   (b.ItemID_YMC = ItemID_YMC) AND (b.date = date))

恩恩，是这样的哈哈，脑子秀逗了。
但是我还有个问题：
“=”后面（）
里面的东西 那是一个单独的查询这个查询前面也没有 a.或者b.或者c.的这些东西。那么他倒是（）里边出来的是什么东西，这两个东西怎么可以相等呢？

只要知道整个(SELECT   MAX(PV) AS Expr1
                     FROM      dbo.DS04_YMC_BaiDuLiuLiang AS c
                     WHERE   (b.ItemID_YMC = ItemID_YMC) AND (b.date = date)) 是个什么结果不就明白了

SELECT DISTINCT TOP (100) PERCENT DATEADD(dd,-1,a.date) as date, a.ItemID_YMC, a.ItemID_YMC2, b.PV
FROM ABC AS a LEFT OUTER JOIN EFG AS b ON a.ItemID_YMC = b.ItemID_YMC AND a.date = b.date AND b.PV = (SELECT MAX(PV) AS Expr1 FROM dbo.DS04_YMC_BaiDuLiuLiang AS c WHERE (b.ItemID_YMC = ItemID_YMC) AND (b.date = date))
红色标识的是代表从DS04_YMC_BaiDuLiuLiang中查询出符合b.ItemID_YMC = ItemID_YMC AND b.date = date这两个条件的最大的PV字段值，因为返回的数量总是一个，所以可以放在“=”的后面，相当于b.PV = 1000（最大值）

谢谢，你太厉害了~~啥都知道  

谢谢