Question

我想有一种更好的方法可以从row_number中获取最后一行，而不是使用T-SQL进行多次嵌套。

我需要订单总数和最后订购日期。说我有以下内容：

DECLARE @T TABLE (PERSON_ID INT, ORDER_DATE DATE)
INSERT INTO @T VALUES(1, '2016/01/01')
INSERT INTO @T VALUES(1, '2016/01/02')
INSERT INTO @T VALUES(1, '2016/01/03')
INSERT INTO @T VALUES(2, '2016/01/01')
INSERT INTO @T VALUES(2, '2016/01/02')
INSERT INTO @T VALUES(3, '2016/01/01')
INSERT INTO @T VALUES(3, '2016/01/02')
INSERT INTO @T VALUES(3, '2016/01/03')
INSERT INTO @T VALUES(3, '2016/01/04')

我想要的是：

PERSON_ID   ORDER_DATE  ORDER_CNT
1           2016-01-03  3
2           2016-01-02  2
3           2016-01-04  4

除了以下内容之外，还有更好的方法吗？

SELECT *
  FROM (
    SELECT *
         , ROW_NUMBER() OVER (PARTITION BY PERSON_ID ORDER BY ORDER_CNT DESC) AS LAST_ROW
      FROM (
        SELECT *
             , ROW_NUMBER () OVER (PARTITION BY PERSON_ID ORDER BY ORDER_DATE) AS ORDER_CNT
          FROM @T
        ) AS A
    ) AS B
WHERE LAST_ROW = 1

Answer 1

是的，您可以使用：

SELECT 
  PERSON_ID, 
  MAX(ORDER_DATE) AS ORDER_DATE, 
  COUNT(*) AS ORDER_CNT 
FROM @T
GROUP BY PERSON_ID

Answer 2

SELECT  a.PERSON_ID
    ,   a.ORDER_DATE
    ,   a.ORDER_CNT
FROM
    (
    SELECT  PERSON_ID
        ,   ORDER_DATE
        ,   rn = ROW_NUMBER () OVER (PARTITION BY PERSON_ID ORDER BY ORDER_DATE DESC)
        ,   ORDER_CNT = COUNT(ORDER_DATE) OVER (PARTITION BY PERSON_ID)
    FROM @T
    ) AS a
WHERE rn = 1
ORDER BY a.PERSON_ID;

使用SQL从ROW_NUMBER获取最后一行

2 个答案: