Mysql查询使用WHEN更新多个条件的多列，并且

Question

我正在将2条记录的sql UPDATE写入2条件。在我运行sql之前，sender_del_flag和receiver_del_flag都是0，但是在运行这个之后，有些值返回null。我想知道它为什么变为null。如何解决这个问题？

UPDATE `messages` SET 
     receiver_del_flag = CASE 
      WHEN `id`='4' AND receiver='92' THEN '1' 
      WHEN `id`='6' AND receiver='92' THEN '1' 
      WHEN `id`='8' AND receiver='92' THEN '1' 
     END, 
     sender_del_flag = CASE 
      WHEN `id`='4' AND sender='92' THEN '1' 
      WHEN `id`='6' AND sender='92' THEN '1' 
      WHEN `id`='8' AND sender='92' THEN '1' 
     END 
    WHERE id IN ('4', '6', '8') 

Answer 1

这解决了这个问题：

UPDATE `messages` SET 
     receiver_del_flag = CASE 
      WHEN `id`='4' AND receiver='92' THEN '1' 
      WHEN `id`='6' AND receiver='92' THEN '1' 
      WHEN `id`='8' AND receiver='92' THEN '1' 
      ELSE receiver_del_flag 
     END, 
     sender_del_flag = CASE 
      WHEN `id`='4' AND sender='92' THEN '1' 
      WHEN `id`='6' AND sender='92' THEN '1' 
      WHEN `id`='8' AND sender='92' THEN '1' 
      ELSE sender_del_flag 
     END 
    WHERE id IN ('4', '6', '8'); 

你where条款越来越排在sender和receiver是92。这些设置正确。它也获取行的值不是92。这些设置为NULL，因为没有ELSE子句。