'WHERE' condition in an UPDATE TRIGGER giving syntax error :mysql version 5.7

Question

我正在使用 mysql 数据库（版本 5.7）。

我使用以下 CREATE 命令创建了一个 table：

CREATE TABLE `attendance` (
  `id` varchar(11) NOT NULL,
  `hash` char(8) NOT NULL,
  `time_in` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `time_out` datetime DEFAULT NULL,
  `time_spent` time DEFAULT NULL,
  `purpose` char(10) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

我有一个带有以下查询的触发器：

DELIMITER $$

CREATE TRIGGER test_trigger 
BEFORE UPDATE ON attendance 
FOR EACH ROW 
BEGIN 
SET NEW.time_spent=TIMEDIFF(NEW.time_out,OLD.time_in) WHERE OLD.time_spent IS NULL; 
END$$

DELIMITER ;

但是mysql给出了以下错误：

ERROR 1064 (42000): 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 'WHERE OLD.time_spent IS NULL; END' at line 1

（where 条件确保只更新当天的记录）

我该如何编写查询？

Answer 1

您不能在触发器中使用带有 SET 的 WHERE 子句。使用 IF 代替：

DELIMITER $$

CREATE TRIGGER test_trigger 
BEFORE UPDATE ON attendance 
FOR EACH ROW 
BEGIN
    IF OLD.time_spent IS NULL THEN
        SET NEW.time_spent = TIMEDIFF(NEW.time_out, OLD.time_in);
    END IF;
END$$

DELIMITER ;

'WHERE' condition in an UPDATE TRIGGER giving syntax error :mysql version 5.7

'WHERE' condition in an UPDATE TRIGGER giving syntax error :mysql version 5.7

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