use constraint or rules that will helps u in this query
we can also use cursor for this for insert

If u Use SQLSERVER 2005. This will helpful to you


CREATE RULE myRule AS @strGrade IN('I','II','III','IV')
GO
CREATE TABLE myTable
   (
	empID	INT,
	empName	VARCHAR(50),
	empGrade	VARCHAR(3),
	empSalary	NUMERIC(9,2)
   );
GO
sp_bindrule myRule, 'myTable.empGrade';
GO


INSERT INTO myTable VALUES(1,'Ganesh','I',59000)   -- Valid
INSERT INTO myTable VALUES(1,'Ganesh','II',89000)  -- Valid
INSERT INTO myTable VALUES(1,'Ganesh','III',99000) -- Valid
INSERT INTO myTable VALUES(1,'Ganesh','IV',259000) -- Valid
INSERT INTO myTable VALUES(1,'Ganesh','V',259000)  -- 
Invalid

create table #test (sno int check(sno in(1,2,3)))

successfull statement:
insert into #test values(3)

failure statement :

insert into #test values(4)
error message:
INSERT statement conflicted with COLUMN CHECK 
constraint 'CK__#test__sno__68E599B5'. The conflict 
occurred in database 'tempdb', 
table '#test________________________________________________
____________________________________________________________
___00000000D7E0', column 'sno'.
The statement has been terminated.