SQL 触发器(学生,课程表,选修表）
触发器是一种 特殊类型的存储过程 ，它不由用户通过命令来执行，而是 在用户对表执行了插入，删除或修改表中数据等操作时激活执行 。可以这样形容： 存储过程像一个遥控*，我们可以根据需要控制它何时爆炸；而触发器却像一个地雷，一旦踩中就会爆炸 。 一
触发器是一种特殊类型的存储过程，它不由用户通过命令来执行，香港服务器，而是在用户对表执行了插入，删除或修改表中数据等操作时激活执行。可以这样形容：存储过程像一个遥控*，我们可以根据需要控制它何时爆炸；而触发器却像一个地雷，一旦踩中就会爆炸。
一.创建触发器
--创建一个名为的触发器,如发现课程表的学时列发生变化时,激活触发器,在屏幕上显示 create trigger Update_course on 课程 for insert,update,delete as if UPDATE(学时) select * from 课程 print update 课程 ，香港虚拟主机，香港虚拟主机
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