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INSERT触发器： 向表中插入数据时被触发
UPDATE触发器：修改表中数据时被触发
DELETE触发器：从表中删除数据时被触发

INSERT 触发器：
在向目标表中插入数据后，会触发该表的INSER触发器，系统自动在内存中创建INSERTED表

UPDATE 触发器：
在向目标表中更新数据后，会触发该表的UPDATE触发器，系统自动在内存中创建DELETED表和INSERTED表，DELETED表存放的是更新前的数据，INSERTED表存放的是更新的数据

Delete 触发器：
在向目标表中删除数据后，会触发该表的Delete 触发器，系统自动在内存中创建DELETED表，DELETED表存放的是删除的数据

DEMO:

Create TRIGGER [dbo].[Trigger]
ON [dbo].BD_Supplier
AFTER INSERT --UPDATE --DELETE
AS
BEGIN
SET NOCOUNT ON
SELECT * FROM INSERTED
SELECT * FROM DELETED
END

--------------------------------------------------------------------
CREATE TRIGGER OrdDet_Insert
ON [Order Details]
FOR INSERT
AS
UPDATE P SET UnitsInStock = P.UnitsInStock – I.Quantity
FROM Products AS P 
INNER JOIN Inserted AS I ON P.ProductID = I.ProductID

--------------------------------------------------------------------
CREATE TRIGGER Category_Delete
ON Categories
FOR DELETE
AS
UPDATE P SET Discontinued = 1
FROM Products AS P 
INNER JOIN deleted AS d ON P.CategoryID = d.CategoryID

--------------------------------------------------------------------
   CREATE TRIGGER dbo.SEOrderEntry_Update
               ON dbo.SEOrderEntry
   FOR UPDATE
   AS
   IF UPDATE (FCommitQty) -- 更新的字段
   BEGIN
      SELECT * FROM inserted
      SELECT * FROM deleted
   END
   GO