Concatenating multiple fetches into a single string

Dear Friends,

I am doing a migration from SQL server to Postgres SQL. A simple select fetches the following names.

select full_name FROM project_members where project_members.project_role_id in (' + @p_res_ids + ') ;

Let us say if the results are

full_name
---------------
David
Postgres
plpgsql

I need to send the out put as David,Postgres,Plsql -- one string, concatenates the fetches from multiple rows. This was handled in SQL server with a cursor.

Can this be handled only by sql manipulation or need to use cursors. If i use cursor in postgres, what is the equivalent of MS SQL Statement
WHILE @@FETCH_STATUS = 0.

please shed some light pls.