MySQL触发器: Prevent Insert by IF statement

Question

我尝试为 MySQL 数据库编写第一个触发器。它应该在当前时间和“容量”中的给定时间戳的上下文中防止在“course_student”上插入(以及稍后更新) ，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；所以可能存在输入错误。

Answer 1

您缺少一些逗号和一些弥补的 sql，并且末尾缺少分隔符。

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 ;