sql。語法選擇執行算術運算

Question

我希望在選擇syntac sql中執行算術運算，如10減5 = 5，但我的選擇不起作用。

select DATEDIFF(MINUTE,on_duty, clock_in) as late, DATEDIFF(MINUTE ,off_duty, clock_out) as Early, late - Early as jajalan from kkpsurabaya 

look image pls

Answer 1

你不能使用函數的結果在同一個選擇，因爲you cannot refer to an alias外SELECT和ORDER BY由於方式的查詢進行解析。你可以調用同一個函數多次：

select DATEDIFF(MINUTE,on_duty, clock_in) as late, 
     DATEDIFF(MINUTE ,off_duty, clock_out) as Early, 
     DATEDIFF(MINUTE,on_duty, clock_in)- DATEDIFF(MINUTE ,off_duty, clock_out) as jajalan 
from kkpsurabaya 

或公共表expreession：

WITH CTE AS 
(
    SELECT DATEDIFF(MINUTE,on_duty, clock_in) as Late, 
    DATEDIFF(MINUTE ,off_duty, clock_out) as Early, 
    t.* 
    FROM kkpsurabaya t 
) 
SELECT Late, Early, Late - Early as jajalan 
FROM CTE