How to separate int and string values in a table?

Question

Hi,

     I have a  table named Itemdetails. There is a column named ItemCode it is initialised as varchar(50). So I entered both int and string values to the column. Now I need to use auto increment operation for the integer values in the column. So I need to get  max(ItemCode)+1 value. For that I need to seperate string and int values. 

Thanks