更改更新触发器以在 MySQL 中插入触发器

Question

我是初学者，正在研究如何从这个 link 计算学生成绩的触发器。 Student_Marks Trigger before update 触发器的查询工作正常。我试图稍微改变一下触发器。我想在插入学生的分数后计算成绩。因此，after 触发而不是 update。我卡住了。

我的查询如下：

DELIMITER 
$$
CREATE TRIGGER `student_marks` 
AFTER INSERT 
ON student FOR EACH ROW

BEGIN 
SET NEW.Total =NEW.SUB1+NEW.SUB2+NEW.SUB3+NEW.SUB4+NEW.SUB5; 
SET NEW.Percentage = NEW.Total/5;
IF NEW.Percentage >=90 THEN
SET NEW.Grade = 'EXCELLENT';
ELSEIF NEW.Percentage>=75 AND NEW.Percentage<90 THEN
SET NEW.Grade = 'VERY GOOD';
ELSEIF NEW.Percentage>=60 AND NEW.Percentage<75 THEN
SET NEW.Grade = 'GOOD';
ELSEIF NEW.Percentage>=40 AND NEW.Percentage<60 THEN
SET NEW.Grade = 'AVERAGE';
ELSE SET NEW.Grade = 'NOT PROMOTED';
END IF;
END;
$$

Answer 1

您必须使用 BEFORE INSERT 而不是 AFTER INSERT 来保存新行的计算值。您不能影响行 AFTER INSERT，因为该行已保存。

DELIMITER $$

CREATE TRIGGER `student_marks` 
BEFORE INSERT ON student_marks FOR EACH ROW
BEGIN 
    SET NEW.Total =NEW.SUB1+NEW.SUB2+NEW.SUB3+NEW.SUB4+NEW.SUB5; 
    SET NEW.Percentage = NEW.Total/5;

    IF NEW.Percentage >=90 THEN
        SET NEW.Grade = 'EXCELLENT';
    ELSEIF NEW.Percentage>=75 AND NEW.Percentage<90 THEN
        SET NEW.Grade = 'VERY GOOD';
    ELSEIF NEW.Percentage>=60 AND NEW.Percentage<75 THEN
        SET NEW.Grade = 'GOOD';
    ELSEIF NEW.Percentage>=40 AND NEW.Percentage<60 THEN
        SET NEW.Grade = 'AVERAGE';
    ELSE 
        SET NEW.Grade = 'NOT PROMOTED';
    END IF;
END;
$$

您还需要更改 TRIGGER 的 table 名称（使用 INSERT ON student_marks 而不是 INSERT ON student）。

demo on dbfiddle.uk

更改更新触发器以在 MySQL 中插入触发器

Changing an update trigger to insert trigger in MySQL

mysql

database-trigger