You need to get the part of Serial Number in column1 and the last 3 signs in column2.
I don't know which database you use. In MS Access or in MS SQL Server you can "ask" your database like this:
SELECT Left([Serial Number],6) As FPartSN, Right([Serial Number],3) As LPartSN
FROM TABLE1;
where TABLE1 is the name of your table.
It whould help you to group duplicated values.