将 NULL 视为 MAX 日期

Question

我需要检索每个客户的 MAX ResponsibleEndDate。如果有 NULL，则将其视为 MAX 日期。

CREATE TABLE example
(Id INT, ClientId INT, ClientName VARCHAR(100), ResponsibleId INT, ResponsibleName VARCHAR(100), ResponsibleStartDate DATE, ResponsibleEndDate DATE);

INSERT INTO example
VALUES
(1, 123, 'John Smith', NULL, NULL, NULL, NULL),
(2, 234, 'Thomas Anderson', 12345, 'Tom Cruise', '2019-04-13', '2020-09-15'),
(3, 234, 'Thomas Anderson', 23456, 'John Travolta', '2020-09-16', '2022-01-15'),
(4, 234, 'Thomas Anderson', 37890, 'Van Damm', '2022-01-16', NULL),
(5, 345, 'Mary Tron', NULL, NULL, NULL, NULL),
(6, 456, 'Jackie Chan', 56789, 'Leo Messi', '2018-05-18', '2022-01-18'),
(7, 567, 'Cristiano Ronaldo', 12345, 'Tom Cruise', '2019-05-28', '2021-08-20'),
(8, 567, 'Cristiano Ronaldo', 37890, 'Van Damm', '2021-07-15', '2022-01-15'),
(9, 567, 'Cristiano Ronaldo', 17956, 'Harry Potter', '2022-01-25', NULL)

我需要的输出：

Id	ClientId	ClientName	ResponsibleId	ResponsibleName	ResponsibleStartDate	ResponsibleEndDate	MaxDate
1	123	John Smith	NULL	NULL	NULL	NULL	NULL
2	234	Thomas Anderson	12345	Tom Cruise	2019-04-13	2020-09-15	NULL
3	234	Thomas Anderson	23456	John Travolta	2020-09-16	2022-01-15	NULL
4	234	Thomas Anderson	37890	Van Damm	2022-01-16	NULL	NULL
5	345	Mary Tron	NULL	NULL	NULL	NULL	NULL
6	456	Jackie Chan	56789	Leo Messi	2018-05-18	2022-01-18	2022-01-18
7	567	Cristiano Ronaldo	12345	Tom Cruise	2019-05-28	2021-08-20	NULL
8	567	Cristiano Ronaldo	37890	Van Damm	2021-07-15	2022-01-15	NULL
9	567	Cristiano Ronaldo	17956	Harry Potter	2022-01-25	NULL	NULL

我的查询：

SELECT *,
    MAX(ResponsibleEndDate)OVER(PARTITION BY ClientId) AS MAX_END_DATE    
FROM example
ORDER BY ClientId, ResponsibleStartDate

Answer 1

聚合函数，在 T-SQL 中，忽略 NULL 值并且 NULL 也被视为具有最低值，而不是最高值.

因此，您需要使用几个函数将 NULL 替换为任意高的值，然后再次 NULL ：

SELECT ClientID,
       ClientName,
       {Rest of your columns},
       NULLIF(MAX(ISNULL(ResponsibleEndDate,'99991231')) OVER (PARTITION BY ClientId),'99991231') AS MAX_END_DATE    
FROM dbo.example
ORDER BY ClientId,
         ResponsibleStartDate;

Answer 2

另一种选择是显式检查 NULL

是否存在

SELECT
  ClientID,
  ClientName,
       {Rest of your columns},
  CASE WHEN COUNT(CASE WHEN ResponsibleEndDate IS NULL THEN 1 END) OVER (PARTITION BY ClientId) = 0
      THEN MAX(ResponsibleEndDate) OVER (PARTITION BY ClientId)
  END AS MAX_END_DATE    
FROM dbo.example
ORDER BY
  ClientId,
  ResponsibleStartDate;

一个细微的变化是 CASE WHEN COUNT(ResponsibleEndDate) = COUNT(*) 因为 COUNT 只会计算 non-null 个值

将 NULL 视为 MAX 日期

Treat NULL as MAX Date

sql

sql-server

date

max