如何在触发器中将一列递增? [英] How can I increment a column by one in a trigger?

问题描述

我需要编写MySQL触发器的帮助.

I need help writing a MySQL trigger.

假设您有一个包含以下表格的学生数据库:

Suppose you have a student database with the following tables:

ENROLLMENT(SSN, CLASS_NO, GRADE)
CLASS(CLASS_NO, CLASS_TITLE, NO_OF_STUDENTS).

如果将新学生添加到该 CLASS_NO 的 ENROLLMENT 表中，我需要编写触发器以将 NO_OF_STUDENTS 增大一.

I need to write a trigger to increase the NO_OF_STUDENTS by one if a new student is added to the ENROLLMENT table for that CLASS_NO.

推荐答案

您可以使用mysql触发器来执行此操作.尝试类似

you can use mysql trigger to do this. Try something like

CREATE TRIGGER 'database_name'.'after_insert_enrollment' AFTER INSERT ON 'ENROLLMENT' 
FOR EACH ROW
BEGIN
UPDATE class SET NO_OF_STUDENTS = NO_OF_STUDENTS +1 WHERE CLASS_NO = NEW.CLASS_NO;
END

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