使用case语句更新时的MySql查询语法错误

Question

如果第一列不为null，我想更新第二列值，否则更新最合适的列。下面是我查询的查询，但此查询给出了语法错误。以下是我的查询

UPDATE messages 
SET  CASE WHEN delete_one IS NULL THEN delete_one = 9600 ELSE delete_two = 9600  END 
WHERE
( message_to = 9600 AND message_from = 8625 ) 
OR 
( message_to = 8625 AND message_from = 9600);

以下是运行此查询后我收到的语法错误

Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'case when delete_one IS NULL THEN delete_one = 9600 ' at line 3

请帮助解决此问题。

提前致谢

Answer 1

CASE Expression必须位于SET的右侧：

UPDATE messages 
SET  delete_two = CASE WHEN delete_one IS NOT NULL THEN 9600  ELSE delete_two END,
delete_one = COALESCE(delete_one,9600) 
WHERE
( message_to = 9600 AND message_from = 8625 ) 
OR 
( message_to = 8625 AND message_from = 9600);

Answer 2

尝试分配CASE表达式：

UPDATE messages 
SET delete_one = COALESCE(delete_one, 9600),
    delete_two = CASE WHEN delete_one IS NULL THEN delete_two ELSE 9600 END 
WHERE
    (message_to = 9600 AND message_from = 8625 ) OR
    (message_to = 8625 AND message_from = 9600);