php - Mysql查询使用WHEN和AND更新具有多个条件的多列

Question

我正在使用 2 个条件将 sql UPDATE 写入 2 个列。在我运行 sql 之前，sender_del_flag 和 receiver_del_flag 都是 0，但是在我运行这个之后一些值返回 null。我想知道为什么它变成了空。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');

您的 where 子句正在获取 sender 和 receiver 为 92 的行。这些设置正确。它还获取值不是 92 的行。这些设置为 NULL，因为没有 ELSE 子句。