创造触发器时出错，求解_Sql Server

创建触发器时出错，求解！
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)
IF @tatal > 30
BEGIN
ROLLBACK
RAISERROR('错误提示',16,1)
END
GO

提示错误如下：
消息 156，级别 15，状态 1，过程 ck_credit，第 12 行
关键字 'IF' 附近有语法错误。
找不到错误原因，求解惑，谢谢！

------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
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

CREATE TRIGGER dbo.ck_credit    ON dbo.sc    AFTER INSERTAS  DECLARE @tatal tinyint  SELECT @tatal=sum(credit)  FROM (  SELECT sno,credit  FROM sc,course  WHERE sc.sno=inserted.sno AND sc.sno=course.sno)tIF @tatal > 30    BEGIN  ROLLBACK  RAISERROR('错误提示',16,1)  ENDGO
------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aCREATE TRIGGER dbo.ck_credit    ON dbo.sc    AFTER INSERTAS  DECLARE @tatal tinyint  SELECT @tatal=sum(credit)  FROM (  SELECT sno,credit  FROM sc,course  WHERE sc.sno=inserted.sno AND sc.sno=course.sno)aIF @tatal > 30    BEGIN  ROLLBACK  RAISERROR('错误提示',16,1)  ENDGO
------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 codeCREATE TRIGGER dbo.ck_credit  ON dbo.sc  AFTER INSERTAS  --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)>30BEGIN  ROLLBACK  RAISERROR('错误提示',16,1)ENDGO