How to Use a correlated subquery to get sum of colums for particular items

How to Use a correlated subquery to get sum of colums for particular items

 select itemid from table1 A  
 where col1 = 'sp'  
 and amt <>  
  (select sum(amt) from table1 B  
   where B.itemid = A.itemid  
   and col1 in ('a','b')  
  )  
 ;