MySQL 触发器：防止通过 IF 语句插入

Question

我尝试为 MySQL 数据库编写我的第一个触发器。它应该防止在当前时间和给定时间戳的上下文中对“course_student”插入（以及稍后更新） “容量”，但我仍然遇到语法错误。

DELIMITER $$

CREATE TRIGGER checkSubscribeTimeCourse 
BEFORE INSERT ON course_student
REFERENCING NEW AS new
FOR EACH ROW 

BEGIN

    IF (SELECT COUNT(*) FROM capacity c, course_capacity cc 
        WHERE c.cid = cc.cid 
        AND cc.cid = new.cid
        AND (c.end >= CURRENT_TIMESTAMP OR c.end IS NULL)
        AND (c.start <= CURRENT_TIMESTAMP OR c.start IS NULL)<1)
    THEN
        SIGNAL SQLSTATE '45000'
        SET MESSAGE_TEXT = 'Error'
    END IF

END

DELIMITER ;

我翻译了所有名字；所以可能有打字错误。

Answer 1

您缺少一些逗号，一些逗号由 sql 组成，末尾缺少分隔符。

DELIMITER $$

CREATE TRIGGER checkSubscribeTimeCourse 
BEFORE INSERT ON course_student
FOR EACH ROW
BEGIN

    IF (SELECT COUNT(*) FROM capacity c, course_capacity cc 
        WHERE c.cid = cc.cid 
        AND cc.cid = new.cid
        AND (c.end >= CURRENT_TIMESTAMP OR c.end IS NULL)
        AND (c.start <= CURRENT_TIMESTAMP OR c.start IS NULL)<1)
    THEN
        SIGNAL SQLSTATE '45000'
        SET MESSAGE_TEXT = 'Error';
    END IF;

END$$

DELIMITER ;

MySQL 触发器：防止通过 IF 语句插入

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