触发器 在学生表中删除学生的同时删除选课表的信息 CREATE TRIGGER students_delete_before BEFORM DELETE ON students FOR EACH ROW BEGIN DELETE FROM sc WHERE Sno=old.Sno; END; 更新选课表信息 CREATE TRIGGER students_update_after AFTER UPDATE ON students FOR EACH ROW BEGIN UPDATE sc SET Sno=new.Sno WHERE Sno=old.Sno; END; 学分录入（成绩大于60） CREATE TRIGGER sc_install_after AFTER UPDATE ON sc FOR EACH ROW BEGIN DECLARE xf SAMLLINT; SELECT Ccredit INTO xf FORM course WHERE Cno=new.Cno; IF new.Grade>=60 THEN UPDATE students SET Scredit+xf WHERE Sno=new.Sno; END IF; END;这段代码找出错误并改正

在第三个触发器中，声明变量的语句中 "SAMLLINT" 应该为 "SMALLINT"。同时，在更新语句后面应该加上 SET 关键字，将修改后的学分值赋值给 Scredit 字段。修改后的代码如下：

CREATE TRIGGER sc_install_after AFTER UPDATE ON sc FOR EACH ROW 
BEGIN 
    DECLARE xf SMALLINT; 
    SELECT Ccredit INTO xf FROM course WHERE Cno=new.Cno; 
    IF new.Grade >= 60 THEN 
        UPDATE students SET Scredit = Scredit + xf WHERE Sno = new.Sno; 
    END IF; 
END;