SqlServer 实现类似Oracle 的before触发器

1. 插入数据前判断数据是否存在

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:		<Author,Name>
-- Create date: <Create Date,>
-- Description:	<Description,>
-- =============================================
alter TRIGGER CategoryExistTrigger 
   ON  ProductCategory
   instead of insert 
AS 

declare @categoryName varchar(50);
BEGIN
	-- SET NOCOUNT ON added to prevent extra result sets from
	-- interfering with SELECT statements.
	SET NOCOUNT ON;

    -- Insert statements for trigger here
    select @categoryName = CategoryName from inserted;
    if exists(select * from ProductCategory where CategoryName =@categoryName)
    begin
    print 'Category exists..'
    end;
    else
    begin
    insert into ProductCategory  select * from inserted;
    end;

END

2. 删除表中数据时需要先删除外键表的数据

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:		<Author,>
-- =============================================
alter TRIGGER DeleteOrderTrigger
   ON  OrderHeader
   instead of delete 
AS 
declare @OrderId varchar(50);
BEGIN

   SET NOCOUNT ON;
   select @OrderId = OrderId from deleted;
   delete from OrderLine where OrderId = @OrderId;
   
END
GO