如何使用CASE語句分配NULL值？

Question

我正在嘗試使用CASE語句在另一個字段為NULL時分配NULL值。

到目前為止，這是我得到的：

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

這應該做你想做的事情：

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