What order are the values being displayed?
Suggestion is read documentation or Google or search within the OBIEE space.
I got the answer , i created another logical column based on the above column and sorted the column value based on the value which it is picking from it worked.
Thanks for your time.
Good. "Basing the Sort for a Logical Column on a Different Column" section of Metadata Repository Builder's Guide for OBIEE describes how it's done.