我正在尝试执行以下触发器:
create trigger t23
on studies
after insert, update, delete
as
begin
REFERENCING NEW ROW NewStudent
FOR EACH ROW
WHEN (30 <= (SELECT SUM(credits) FROM Studies)
DELETE FROM NewStudent N
WHERE N.spnr = NewStudent.spnr
end
我正在尝试创建一个触发器,只有在学分为&lt;或==到'30'。 “Credits”是int类型。
我在尝试实现此触发器时遇到了很多错误。我真的尝试了一切,而且我没有选择。这个领域的专家可以指出我正确的方向吗?
答案 0 :(得分:17)
CREATE TRIGGER MSDN文档中的“使用DML AFTER触发器强制执行PurchaseOrderHeader和Vendor表之间的业务规则”的示例确实可以满足您的需求:
USE AdventureWorks2008R2;
GO
IF OBJECT_ID ('Purchasing.LowCredit','TR') IS NOT NULL
DROP TRIGGER Purchasing.LowCredit;
GO
-- This trigger prevents a row from being inserted in the Purchasing.PurchaseOrderHeader table
-- when the credit rating of the specified vendor is set to 5 (below average).
CREATE TRIGGER Purchasing.LowCredit ON Purchasing.PurchaseOrderHeader
AFTER INSERT
AS
DECLARE @creditrating tinyint, @vendorid int;
IF EXISTS (SELECT *
FROM Purchasing.PurchaseOrderHeader p
JOIN inserted AS i
ON p.PurchaseOrderID = i.PurchaseOrderID
JOIN Purchasing.Vendor AS v
ON v.BusinessEntityID = p.VendorID
WHERE v.CreditRating = 5
)
BEGIN
RAISERROR ('This vendor''s credit rating is too low to accept new purchase orders.', 16, 1);
ROLLBACK TRANSACTION;
RETURN
END;
此处的关键是ROLLBACK TRANSACTION
,只需调整示例以满足您的需求即可。
编辑:这应该可以完成你想要的,但我没有测试过,所以你的里程可能会有所不同。
create trigger dbo.something after insert as
begin
if exists ( select * from inserted where sum(credits) > 30 )
begin
rollback transaction
raiserror ('some message', 16, 1)
end
end
基于一些假设的另一个编辑(请注意我现在编写了这个脚本,因为我现在无法测试它):
create table dbo.students
(
student_id int not null,
name varchar (50) not null
)
create table dbo.courses
(
course_id int not null,
name varchar (50) not null,
required_credits int not null
)
create table dbo.results
(
student_id int not null,
course_id int not null,
course_result int not null
)
create trigger dbo.check_student_results on dbo.results after insert as
(
declare @check int
select @check = count(*)
from inserted as a
join dbo.courses as b on b.course_id = a.course_id
where b.required_credits > a.course.result
if @check <> 0
begin
rollback transaction
raiserror('The student did not pass the course.', 16, 1)
end
)
这样,当您在dbo.results
表中插入记录时,约束会检查学生是否已通过课程,并在适当时取消插入。但是,最好在应用程序层中检查这些内容。