[英]Create a trigger for a table that fills a column in the same table whenever a new record is inserted or updated and meets the condition
[英]How to copy a column value to other column of same database table whenever a new record is inserted?
我有以下數據庫表:
Book {Id(primary Key), Name, TotalNoOfCopies, NoOfCopiesAvailable}
我希望每當插入新記錄/行時,列NoOfCopiesAvailabe包含的值與列TotalToOfCopies中的值相同。
我嘗試使用以下成功觸發器:
for insert
as declare @id nvarchar(10),@name varchar(50),@author varchar(40),@totalNoOfCopies tinyint, @availableNoOfCOpies tinyint;
select @id=i.Id from inserted i;
select @name=i.Name from inserted i;
select @author=i.Author from inserted i;
select @totalNoOfCopies=i.TotalNoOfCopies from inserted i;
select @availableNoOfCopies=i.TotalNoOfCopies from inserted i;
delete from Book where Id=@id;
insert into Book values(@id,@name,@author,@totalNoOfCopies,@availableNoOfCOpies);
但它執行3筆交易:
1.用於插入新記錄
2.用於刪除該新記錄
3.用於插入具有NoOfCopiesAvailable = TotalNoOfCopies的新記錄
例如:
Insert into Book values('123','Book','Author',5,null)
訊息:
受影響1行
受影響1行
受影響1行
我想知道單筆交易中是否有任何辦法?
您是否需要INSTEAD OF INSERT觸發器:
CREATE TRIGGER Book_i ON Book
INSTEAD OF INSERT
AS
BEGIN
INSERT INTO Book (
Id,
Name,
TotalNoOfCopies,
NoOfCopiesAvailable
) SELECT
Id,
Name,
TotalNoOfCopies,
TotalNoOfCopies
) FROM
INSERTED
END
GO
顯然是優雅的。
我寧願修復表設計,而改用NumberOfCopiesSold,默認情況下可以為0。
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