如何用CASE语句分配NULL值？

Question

我想使用CASE语句在另一个字段为NULL时分配NULL值。

到目前为止，这是我得到：

UPDATE PunchintervalFinal 
SET INDTTIME_LUNCH = (SELECT CASE 
            WHEN PunchintervalFinal.INDTTIME2 IS NULL THEN 
            NULL 
           END 
         FROM PUNCHBRIDGE A 
         WHERE A.EMPLOYEE = PunchintervalFinal.EMPLOYEE 
           AND A.PUNCHDATE = PunchintervalFinal.PUNCHDATE 
           AND PunchintervalFinal.EMPLOYEE = '500018') 

Answer 1

这应该做你正在尝试做的：

UPDATE PunchintervalFinal 
SET INDTTIME_LUNCH = NULL 
FROM PunchintervalFinal 
    INNER JOIN PUNCHBRIDGE A ON A.EMPLOYEE = PunchintervalFinal.EMPLOYEE 
WHERE PunchintervalFinal.EMPLOYEE = '500018' 
    AND A.PUNCHDATE = PunchintervalFinal.PUNCHDATE 
    AND PunchintervalFinal.INDTTIME2 IS NULL