Question

如何添加强制同一个表中两列值相同的约束？

我希望学生班级与学生成绩匹配。

/*Student Grade = Student Class Grade constraint "BEFORE INSERT" */ 
delimiter //    
CREATE TRIGGER StCGradeCheckBIN BEFORE INSERT ON  STUDENT
FOR EACH ROW
BEGIN
    IF new.Class_Grade <> Grade THEN
    SIGNAL SQLSTATE '10000'
        SET MESSAGE_TEXT = 'Error while filling the Class Grade faild! It is must match the Student.Grade feild';
    END IF;
END;
// delimiter ;


/*Student Grade = Student Class Grade constraint "BEFORE UPDATE" */ 

delimiter //    
CREATE TRIGGER StCGCheckBUP BEFORE UPDATE ON  Student
FOR EACH ROW
BEGIN
    IF new.Class_Grade <> Grade THEN
    SIGNAL SQLSTATE '10000'
        SET MESSAGE_TEXT = 'Error while Updating the Class Grade feild! It is must mathc  the Student.Grade feild';
    END IF;
END;
// delimiter ;

此触发器不起作用，在插入STUDENT表

期间会导致此错误

Error Code: 1054. Unknown column 'Grade' in 'field list'

使用mysql workbench 6.3

提前致谢

Answer 1

尚未发表评论，但如果两列必须相同，为什么还需要第二列？它不会用于任何目的。

Answer 2

问题在于触发器无法理解Grade。因为它们位于同一个表中，我认为您可以使用new.来限定名称：

delimiter //    
CREATE TRIGGER StCGradeCheckBIN BEFORE INSERT ON  STUDENT
FOR EACH ROW
BEGIN
    IF new.Class_Grade <> new.Grade THEN
--------------------------^
    SIGNAL SQLSTATE '10000'
        SET MESSAGE_TEXT = 'Error while filling the Class Grade faild! It is must match the Student.Grade feild';
    END IF;
END;
// delimiter ;

同一个表中的两列必须匹配 - Mysql

2 个答案: