[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?
我有以下数据库表:
Book {Id(primary Key), Name, TotalNoOfCopies, NoOfCopiesAvailable}
我希望每当插入新记录/行时,列NoOfCopiesAvailabe包含的值与列TotalToOfCopies中的值相同。
我尝试使用以下成功触发器:
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);
但它执行3笔交易:
1.用于插入新记录
2.用于删除该新记录
3.用于插入具有NoOfCopiesAvailable = TotalNoOfCopies的新记录
例如:
Insert into Book values('123','Book','Author',5,null)
讯息:
受影响1行
受影响1行
受影响1行
我想知道单笔交易中是否有任何办法?
您是否需要INSTEAD OF INSERT触发器:
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
显然是优雅的。
我宁愿修复表设计,而改用NumberOfCopiesSold,默认情况下可以为0。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.