Question

我有一个查询

Select Id,DeviceId,TankCount,Tank1_Level,Tank2_Level,ReadTime from Table 



  Id  TankCount   DeviceId  Tank1_Level   Tank2_Level    ReadTime

   1    1           123            20         50         2014-11-07 14:39:33.277
   2    2           456            52         78         2014-11-07 14:39:33.277
   3    1           789            44         50         2014-11-07 14:39:33.277

Tank2_Level在所有TankCount = 1行中为50。

当值等于50时，我不想显示Tank2_Level。

TankCount int，Tank1_Level int，Tank2_Level int。

Id  TankCount   DeviceId        Tank1_Level   Tank2_Level                   ReadTime

   1    1           123            20         null or empty         2014-11-07 14:39:33.277
   2    2           456            52         78                    2014-11-07 14:39:33.277
   3    1           789            44         null or empty         2014-11-07 14:39:33.277

Answer 1

SELECT Id,
DeviceId,
TankCount,
Tank1_Level,
CASE WHEN Tank2_Level = '50' and TankCount != '2' 
     THEN NULL 
     ELSE Tank2_Level 
     END AS [Tank2_Level],
ReadTime 
FROM table

Answer 2

Tank2_Level是数字还是字符串？我假设它是一个数字：

select <other columns>,
       (case when Tank2_Level = 50 
             then 'null or empty' 
             else cast(Tank2_Level as varchar(255))
        end) as Tank2_Level
from . . .;

Answer 3

SELECT Id,
DeviceId,
TankCount,
Tank1_Level,
CASE WHEN TankCount = 1 AND Tank2_Level = '50' THEN NULL ELSE Tank2_Level END AS Tank2_Level,
ReadTime 
FROM Table

Answer 4

SELECT Id
    ,DeviceId
    ,TankCount
    ,Tank1_Level
    ,(CASE Tank2_Level WHEN 50 THEN NULL
        ELSE Tank2_Level END)
    ,ReadTime
FROM TABLE

Answer 5

您可以使用IIF来简化它

Select 
      Id,
      DeviceId,
      TankCount,
      Tank1_Level,
      iif((Tank2_Level=50 and TankCount=1),null,Tank2_Level) as Tank2_Level,
      ReadTime
from Table

Answer 6

SELECT Tank2_Level = CASE WHEN TankCount >= 2 THEN Tank2_Level END
FROM Table

如何在SQL中使用Case？

6 个答案: