CREATE TRIGGER dbo.ck_credit  
  ON dbo.sc  
  AFTER INSERT
AS  
DECLARE @tatal tinyint  
SELECT @tatal=sum(credit)  
FROM (
  SELECT sno,credit
  FROM sc,course
  WHERE sc.sno=inserted.sno AND sc.sno=course.sno)t
IF @tatal > 30  
  BEGIN
  ROLLBACK
  RAISERROR('错误提示',16,1)
  END
GO

------解决方案--------------------
CREATE TRIGGER dbo.ck_credit 
ON dbo.sc 
AFTER INSERT
AS 
DECLARE @tatal tinyint 
SELECT @tatal=sum(credit) 
FROM (
 SELECT sno,credit
 FROM sc,course,inserted
 WHERE sc.sno=inserted.sno AND sc.sno=course.sno) A
IF @tatal > 30 
 BEGIN
 ROLLBACK
 RAISERROR('错误提示',16,1)
 END
GO

------解决方案--------------------
SQL code
---查询表要取别名a
CREATE TRIGGER dbo.ck_credit  
  ON dbo.sc  
  AFTER INSERT
AS  
DECLARE @tatal tinyint  
SELECT @tatal=sum(credit)  
FROM (
  SELECT sno,credit
  FROM sc,course
  WHERE sc.sno=inserted.sno AND sc.sno=course.sno)a
IF @tatal > 30  
  BEGIN
  ROLLBACK
  RAISERROR('错误提示',16,1)
  END
GO

------解决方案--------------------
CREATE TRIGGER dbo.ck_credit  
 ON dbo.sc  
 AFTER INSERT
AS  
--DECLARE @tatal tinyint  
--SELECT @tatal=sum(credit)  
IF ( SELECT sum(T.credit)
 FROM (
 SELECT sno,credit
 FROM sc,course,inserted
 WHERE sc.sno=inserted.sno AND  
 sc.cno=course.cno) AS T) >30
--IF @tatal > 30  
BEGIN
ROLLBACK
RAISERROR('错误提示',16,1)
END
GO

------解决方案--------------------

SQL code

CREATE TRIGGER dbo.ck_credit  
ON dbo.sc  
AFTER INSERT
AS  
--DECLARE @tatal tinyint  
IF (SELECT sum(credit所在的表名.credit)  
FROM (
  SELECT sno,credit
  FROM sc,course,inserted--少了一个表啊，我给你加上你又不看
  WHERE sc.sno=inserted.sno AND sc.sno=course.sno) as T)>30
BEGIN
  ROLLBACK
  RAISERROR('错误提示',16,1)
END
GO