如何在SQL Select语句中使用If else

Question

我有下面的select语句。

WITH cte AS 
(
    SELECT MAX(logDate) AS Daily 
    FROM PhysicalDriveSize 
    GROUP BY DATEADD(m, DATEDIFF(m, 0, logDate), 0) 
) 
SELECT CAST(MIN(t.logDate) AS DATE) AS [Date], Drive, MIN(t.Free) AS [PercentagFree] 
FROM PhysicalDriveSize AS t 
JOIN cte AS m 
ON t.logDate = m.Daily 
WHERE t.Free <= 10 AND t.Free >= 0 
GROUP BY Drive, logDate 

我想根据结果做一些操作，例如：

WITH cte AS 
(
    SELECT MAX(logDate) AS Daily 
    FROM PhysicalDriveSize 
    GROUP BY DATEADD(m, DATEDIFF(m, 0, logDate), 0) 
) 
SELECT MIN(t.Free) AS [PercentagFree] 
FROM PhysicalDriveSize AS t 
JOIN cte AS m 
ON t.logDate = m.Daily 
WHERE t.Free <= 10 AND t.Free >= 0 
GROUP BY Drive, logDate 
IF t.Free <= 10 AND t.Free >= 5 
PRINT 'Warning' 
Else 
PRINT 'Critical' 

我得到下面的错误，如果我if语句执行：

Msg 4104, Level 16, State 1, Line 13 The multi-part identifier "t.Free" could not be bound. Msg 4104, Level 16, State 1, Line 13 The multi-part identifier "t.Free" could not be bound 

我怎么能搞，如果没有错误的语句？

Answer 1

尝试使用case when then这样的：

WITH cte AS 
(
    SELECT MAX(logDate) AS Daily 
    FROM PhysicalDriveSize 
    GROUP BY DATEADD(m, DATEDIFF(m, 0, logDate), 0) 
) 
SELECT MIN(t.Free) AS [PercentagFree], 
case when t.Free <= 10 AND t.Free >= 5 then 'Warning' 
    else 'Critical' end 
FROM PhysicalDriveSize AS t 
JOIN cte AS m 
ON t.logDate = m.Daily 
WHERE t.Free <= 10 AND t.Free >= 0 
GROUP BY Drive, logDate 

编辑：

如果你想发送的消息，你可以尝试创建一个临时变量像

DECLARE @x int; 
WITH cte AS 
(
    SELECT MAX(logDate) AS Daily 
    FROM PhysicalDriveSize 
    GROUP BY DATEADD(m, DATEDIFF(m, 0, logDate), 0) 
) 
SELECT @x = MIN(t.Free) AS [PercentagFree] 
FROM PhysicalDriveSize AS t 
JOIN cte AS m 
ON t.logDate = m.Daily 
WHERE t.Free <= 10 AND t.Free >= 0 
GROUP BY Drive, logDate 
if(@x is not null) 
    PRINT 'Warning' 
Else 
    PRINT 'Critical' 

Answer 2

你可以这样使用：

IF(t.Free <= 10 AND t.Free >= 0, 'Warning', 'Critical') as free