SQL & PL/SQL

Hello Friends,

I have a string like 'asdfgf,pqrstu,,asff,,prquste,'

Need to convert into a single comma seperated string like 'asdfgf,pqrstu,asff,prquste,'

I have used RTRIM('asdfgf,pqrstu,,asff,,prquste,' , ',') but commas in between the string is not removed but only on the right side of the string

select RTRIM('asdfgf,pqrstu,,asff,,prquste,' , ',') from dual ;

I want in a single select statement.

Please advice.

Thanks/Kumar