Oracle Query获取max_column的最大值，如果该列中存在null，则应返回该行

Question

我遇到类似于在delete_reason_！='deleted'时读取max（end_time_）的情况，但是当end_time_为null时，查询应仅返回第2行。

SELECT MAX(END_TIME_) FROM TASK_HISTORY WHERE DELETE_REASON_ != 'deleted'

回到第一排。但是，我想要的结果应该返回第二行。根据Oracle文档，max，sum，min等聚合函数不应该考虑与Count不同的空值。

如果出现null，是否有办法将Null值设为max;否则，max（end_time_）应该是我想要的输出。

任何帮助将不胜感激。

谢谢。

Answer 1

如果我理解正确，这里有一个选项：

SQL> alter session set nls_date_format = 'dd.mm.yyyy';

Session altered.

SQL> with test (end_time_, delete_reason_) as
  2  (select date '2017-12-13', 'completed' from dual union
  3   select null, null from dual union
  4   select date '2017-12-12', 'deleted' from dual union
  5   select date '2018-01-05', 'unknown' from dual
  6  ),
  7  inter as
  8  (select row_number() over (order  by end_time_ desc) rn,
  9   end_time_, delete_reason_
 10   from test
 11   where nvl(delete_reason_, 'x') <> 'deleted'
 12  )
 13  select end_time_ From inter
 14  where rn = 1;

END_TIME_
----------
NULL

SQL>
SQL> with test (end_time_, delete_reason_) as
  2  (select date '2017-12-13', 'completed' from dual union
  3  -- select null, null from dual union
  4   select date '2017-12-12', 'deleted' from dual union
  5   select date '2018-01-05', 'unknown' from dual
  6  ),
  7  inter as
  8  (select row_number() over (order  by end_time_ desc) rn,
  9   end_time_, delete_reason_
 10   from test
 11   where nvl(delete_reason_, 'x') <> 'deleted'
 12  )
 13  select end_time_ From inter
 14  where rn = 1;

END_TIME_
----------
05.01.2018

SQL>

Answer 2

最后，当我使用max（）函数时，我得到了一个像这样的查询来实现null值而不是date。

SELECT task_def_key_
     , CASE WHEN MAX(CASE WHEN end_time_ IS NULL THEN 1 ELSE 0 END) = 0 THEN MAX(end_time_) END
FROM TASK_HISTORY WHERE DELETE_REASON_ != 'deleted'
GROUP BY task_def_key_

Answer 3

从*中选择*（从TASK_HISTORY中选择*，其中DELETE_REASON_！=“由end_time desc删除”订单），其中rownum = 1

这将解决您的问题