The WM_CONCAT
function (if included in your database, pre Oracle 11.2) or LISTAGG
(starting Oracle 11.2) should do the trick nicely. For example, this gets a comma-delimited list of the table names in your schema:
select listagg(table_name, ', ') within group (order by table_name)
from user_tables;
or
select wm_concat(table_name)
from user_tables;
More details/options
Link to documentation