查询:CREATE TRIGGER students_update BEFORE UPDATE ON students FOR EACH ROW BEGIN IF OLD.sid, NEW.sid THEN SIGNAL SQLSTATE '45000' SET...错误代码: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ', NEW.sid THEN SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = "禁止修改�' at line 5
时间: 2023-07-09 09:30:26 浏览: 42
根据您提供的 SQL 语句,我发现语法错误在于 `IF` 语句的条件判断部分写法不正确。应该是判断 `OLD.sid <> NEW.sid`,即旧的学号不等于新的学号,而不是 `OLD.sid, NEW.sid`。同时,`MESSAGE_TEXT` 前面应该加上冒号 `:`。修改后的 SQL 语句应该如下:
```
CREATE TRIGGER students_update BEFORE UPDATE ON students FOR EACH ROW
BEGIN
IF OLD.sid <> NEW.sid THEN
SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = "禁止修改学号";
END IF;
END;
```
这个触发器会在更新 `students` 表中的数据之前执行,并检查是否修改了学生的学号。如果修改了,则会抛出一个异常信号,并提示“禁止修改学号”。
相关问题
DELIMITER // CREATE TRIGGER students_delete BEFORE DELETE ON students FOR EACH ROW BEGIN IF old.sid IN (SELECT sid FROM selected ) THEN signal SQLSTATE '50001' SET message_text ="该学号有选课,禁止删除!"; END IF; DELIMITER ;
根据您提供的 SQL 语句,这是一个在 MySQL 数据库中创建触发器的语句。这个触发器会在 `students` 表中有数据被删除之前触发,并检查该学生的学号是否在 `selected` 表中出现过,如果出现过,则会抛出一个异常信号,并提示该学号有选课,禁止删除。
不过,您的 SQL 语句中缺少了设置 `DELIMITER` 的语句,因此执行会出错。正确的语句应该是:
```
DELIMITER //
CREATE TRIGGER students_delete BEFORE DELETE ON students FOR EACH ROW
BEGIN
IF OLD.sid IN (SELECT sid FROM selected) THEN
SIGNAL SQLSTATE '50001' SET MESSAGE_TEXT = "该学号有选课,禁止删除!";
END IF;
END//
DELIMITER ;
```
这样设置之后,执行该语句即可在 MySQL 数据库中成功创建触发器。
查询:create trigger students_delite before delete on students for each row begin if old.sid in (select sid from selected ) than signa...错误代码: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'than signal sqlstate '50001' set message_text ="该学号有选课,禁止删�' at line 4
根据您提供的 SQL 语句,我发现语法错误在于 `than` 应该是 `then`,同时 `message_text` 前面应该加上冒号 `:`。修改后的 SQL 语句应该如下:
```
CREATE TRIGGER students_delete BEFORE DELETE ON students FOR EACH ROW
BEGIN
IF OLD.sid IN (SELECT sid FROM selected) THEN
SIGNAL SQLSTATE '50001' SET MESSAGE_TEXT = "该学号有选课,禁止删除";
END IF;
END
```