mysql中创建插入触发器。为授课表teaching创建插入触发器teaching_insert。向teaching表添加数据时,需要检测tno和cno是否在教师表和课程表中存在。若不存在则向两个表各添加一条记录。创建之后测试触发器是否有效
时间: 2024-02-20 12:57:21 浏览: 23
好的,可以按照以下步骤创建插入触发器teaching_insert:
1. 创建插入触发器
```mysql
CREATE TRIGGER teaching_insert
BEFORE INSERT ON teaching
FOR EACH ROW
BEGIN
DECLARE tno_count INT;
DECLARE cno_count INT;
SELECT COUNT(*) INTO tno_count FROM teacher WHERE tno = NEW.tno;
SELECT COUNT(*) INTO cno_count FROM course WHERE cno = NEW.cno;
IF tno_count = 0 THEN
INSERT INTO teacher (tno, tname) VALUES (NEW.tno, '');
END IF;
IF cno_count = 0 THEN
INSERT INTO course (cno, cname) VALUES (NEW.cno, '');
END IF;
END;
```
2. 执行插入操作,测试触发器
```mysql
INSERT INTO teaching (tno, cno) VALUES ('T001', 'C001');
```
该操作会向teaching表中插入一条记录,同时检查tno和cno是否在teacher表和course表中存在,若不存在则向两个表中各插入一条记录。
之后可以通过查询teacher表和course表验证是否插入了新记录。