SQL & PL/SQL

Hi,Could you please help me out to compare 2 comma-separated columns(previous_code&current_code) and split the dropped values into DROPPED_CODE  column.I'm working on 11g.Here I have given sample table and data as well.

Create table t1

(id number(10),

previous_code varchar2(200),

current_code varchar2(200),

dropped_code varchar2(200)

);

insert into t1 values (1,'ABC,CDE,FGH','ABC,CDE',NULL);

insert into t1 values(1,'ABC,CDE,FGH','ABC',NULL);

insert into t1 values (1,'ABC,CDE,FGH','CDE',NULL);

COMMIT;

I have to compare PREVIOUS_CODE & CURRENT_CODE Column values and update into DROPPED_CODE field as below.

Thanks,

Jai