问题描述
所以我尝试使用 CROSS APPLY
,但似乎无法正确使用。
SELECT COL1,COL2
FROM dbo.tableA AS A
WHERE COL3 = (SELECT MAX(COL4)
FROM dbo.tableA AS B
WHERE A.COL1 = B.COL1) AS SUB
我试试这个:
SELECT COL1,COL2
FROM dbo.tableA AS A
CROSS APPLY (SELECT MAX(COL4) AS MAX_DATE
FROM TABLEA AS B
WHERE A.COL1 = B.COL1) AS SUB
但是当我使用 CROSS APPLY
时,我总是返回更多的行。我的错误在哪里?
解决方法
如果您希望两个查询相同,您在第二个查询中缺少 WHERE
:
SELECT COL1,COL2
FROM dbo.tableA AS A
CROSS APPLY (SELECT MAX(COL4) AS MAX_DATE
FROM TABLEA AS B
WHERE A.COL1 = B.COL1) AS SUB
WHERE A.COL3 = SUB.MAX_DATE;
,
除了 APPLY
重写之外,因为这是一个自连接,所以它也可以使用 MAX
窗口聚合来完成:
SELECT COL1,COL2
FROM (
SELECT *,MAX(COL4) OVER (PARTITION BY COL1) AS mx
FROM dbo.tableA
) AS A
WHERE COL3 = mx