案例查询中基于计数的返回值答案

【问题标题】：Return value based on count in a case query案例查询中基于计数的返回值
【发布时间】：2021-06-11 06:19:30
【问题描述】：

我很期待你对这个请求的意见，看起来超级简单，但我一个人想不通。

如果表列part_status有一个值，则返回；否则返回“很多”。

场景 1 表格数据：

Part_Status
'A'
'A'
'A'

Part_Status
'A'

场景2表格数据：

Part_Status
'A'

在此处返回 col1 值

Part_Status
'A'

场景 3 表格数据：

Part_Status
'A'
'E'

返回值

Part_Status
'Many'

第一个想法是用例，如果计数的数量大于 1，则返回 'many' 但从不打印：

select DISTINCT case
     when count(PART_STATUS) > 1 THEN
      'MANY'
     ELSE
      PART_STATUS
   end
from (select DISTINCT Part_Status
      from Inventory_Part
     where part_status IN ('A','E')
     )
GROUP BY PART_STATUS

Part_Status
'A'
'E'

在第二个想法中，我得到了 'Many' 工作，但单个结果为 NULL

select CASE
     WHEN COUNT(PART_STATUS) > 1 THEN
      'Many'
   end AS "PART_STATUS"
FROM (select DISTINCT Part_Status
      from Inventory_Part
     where part_status IN ('A', 'E'))

Part_Status 
'Many'

那么，如何将两者结合起来呢？

【问题讨论】：

标签： oracle select count case

【解决方案1】：

我可以解决它。无论如何，我不相信这是聪明的方法。

select CASE
         when "cnt" > 1 THEN
          'Many'
         when "cnt" = 1 THEN
          PART_STATUS
       end
  from (select rownum AS "cnt", PART_STATUS
          FROM (select DISTINCT Part_Status
                  from Inventory_Part
                 where part_status IN ('A', 'E'))
         ORDER BY ROWNUM DESC)

 fetch first row only

【讨论】：

【解决方案2】：

这样的？

SQL> with test (part_status) as
  2    (select 'A' from dual union all
  3     select 'A' from dual
  4    )
  5  select distinct
  6         case when (select count(distinct part_status) from test) > 1 then 'Many'
  7              else part_status
  8         end
  9  from test;

CASE
----
A

SQL> with test (part_status) as
  2    (select 'A' from dual union all
  3     select 'E' from dual
  4    )
  5  select distinct
  6         case when (select count(distinct part_status) from test) > 1 then 'Many'
  7              else part_status
  8         end
  9  from test;

CASE
----
Many

SQL>

【讨论】：

让我检查一下。今天晚些时候我会回来找你的！谢谢！