SQL & PL/SQL

Dears ,

I have an old table where to code grouped by text as shown below

means serial 4 is a group of serial 2 and 3  and serial 6 group of 1 and 5

i would like to get the bleow output, which create extra column in select statement to show me the serial is belong to which group

CREATE TABLE SPLIT_COMMA  (SERIAL NUMBER,COMPANATION VARCHAR2(20),DESCRIPTION VARCHAR2(50));

INSERT INTO SPLIT_COMMA VALUES (1,'','SHOP1');

INSERT INTO SPLIT_COMMA VALUES (2,'','SHOP2');

INSERT INTO SPLIT_COMMA VALUES (3,'','SHOP3');

INSERT INTO SPLIT_COMMA VALUES (4,'3,2','SHOP4');

INSERT INTO SPLIT_COMMA VALUES (5,'','SHOP5');

INSERT INTO SPLIT_COMMA VALUES (6,'5,1','SHOP6');

INSERT INTO SPLIT_COMMA VALUES (7,'','SHOP7');

help please.