SQL数据库建立触发器,在想表中插入数据之前检测有没有相同的记录,有则删除后再插入

create trigger [dbo].[delete] on [dbo].[表A] instead of delete as begin if not exists (select count(*) from B where 登记号 = 条件) insert 表B---插入语句 else delete 表B where 登记号 = 条件 insert 表B ---插入语句 end