mysql - 简单的触发抛出错误并停止执行

Question

我在 MySQL 中有这个触发器

DROP TRIGGER IF EXISTS BeforeGivingRight;
DELIMITER $$
CREATE TRIGGER BeforeGivingRight
BEFORE INSERT ON right_code 
FOR EACH ROW
BEGIN
    DECLARE num_rows INT NULL;
    SELECT count(right_code) FROM valid_rights WHERE right_code  =
                                            new.user_right.right INTO num_rows;
    
    IF num_rows = 0
    THEN
        set msg = concat('Error: That right is not allowed!',
                                      cast(new.user_right.right as char));
        signal sqlstate '45000' set message_text = msg;
    END IF;
END $$
DELIMITER ;

它给了我这个错误

#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 'NULL; SELECT
    count(right_code) FROM valid_rights WHERE right_code  = new.user_' at line 5 

这里出了什么问题？我想做的是，在插入某些权限(例如 201)之前，使用触发器检查 valid_rights 是否存在。

Answer 1

您错过了关键字DEFAULT。使用 0 而不是 NULL。

DECLARE total_sale INT DEFAULT 0;

<强> See HERE: Variables in Stored Procedures