Currently there is no dircet option to merge all tables at a schema Level.
I hvae writtent a small procedure to do this this will work.
In my example Below the DINESH"."MM_TABLE has the list of tables that has to be merged,replace that table with your own table and run this Procedure.
Note: Merge is a costly operation, please be carefull and keep your system admin informed about your action.
create procedure DB_OPERATIONS2
as
begin
declare v_count integer;
declare v_index integer;
declare v_table char(40);
declare clm_name varchar (50);
declare vc_sql_merge varchar(4096);
declare vc_sql_part varchar(4096);
declare vc_sql_load varchar(4096);
declare vc_merge_part varchar(4096);
--MM_TABLE is the table which has all the tables belongs to MM module
DECLARE CURSOR c_cursor1 for select table_name from "DINESH"."MM_TABLE";
--Opening the cursor to acess each table
for cur_row as c_cursor1 DO
v_table := cur_row.TABLE_NAME;
vc_merge_part := ('alter table ' ||:v_table || ' merge PARTITIONS');
exec(:vc_merge_part);
--loading the table from memory
end for;
end;