Hello 
this might be a very common question. How to concatenate string belonging to group by clause.
A similar question was asked somewhere here
2074419
but the suggested method ( given on that page as well as this link 
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:2196162600402
) only works when the group by is an number type. 
Like the exmple used on above page has group by deptno.
But in my case its like ...both columns are varchar 
locationid employeeName
AA Robert
AA Jennifer
AB Walsh
AC Sophie
AB David
AB Neha
and I need something like this
locationID empleeList
AA Robert, Jennifer
AB Walsh,David, Neha
AC Sophie
when I execute ..it just never returns the control and keeps executing