如何使用CASE语句分配NULL值？

Question

我正在尝试使用CASE语句在另一个字段为NULL时分配NULL值。

到目前为止，这是我得到的：

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

这应该做你想做的事情：

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