Question

我理解触发器的想法，但对如何使用它来施加约束有点困惑。例如，我有两个表：一个student表和一个book_order表，显示学生订购的书。

我想创建一个触发器，用于检查带有图书订单的学生是否无法从学生表中删除。

Answer 1

不确定为什么你会这样做，除非你想写日志或事情发生但是......

create TRIGGER Del_Student
ON dbo.Student
INSTEAD OF DELETE
AS
BEGIN
   Declare @cnt int
   Select @cnt = count(*) from deleted d 
     Inner Join BookOrders o on d.studentId = o.studentId
   if (@cnt > 0)
   BEGIN
      RAISERROR ('Deletions not allowed from this table when bookorders exist for student)',     16, 1)
   END  
END

使用SQL Server触发器来施加约束

1 个答案: