Concatenate columns with distinct values in oracle

Question

Hello Gurus,
My table structre look like follwoing:
TankListUS    TankListCanada     TankListIndia
T111||T222       T444||T222            T555
Now when I run the query:
select (TL.TankListUS || '||'  || TL.TankListCanada || '||'  || TL.TankListIndia)as "OverallSummary" from TankListTL
I get output as
T111||T222||T444||T222||T555
But I don't need duplicate of tanks. I need my output as:
T111||T222||T444||T555
Is this possible?

Answer 1

May be this can be done in regexp..
If you are in 11g, I just tried hard way... (split, remove dups and concatenate again....) -- not elegant, but works for your test case. (this can be simplified as well )
WITH t AS
        (SELECT 'T111||T222' tanklistus,
                'T444||T222' tanklistcanada,
                'T555' tanklistindia
           FROM DUAL),
     tt AS
        (SELECT REPLACE (
                      TL.TankListUS
                   || ','
                   || TL.TankListCanada
                   || ','
                   || TL.TankListIndia,
                   '||',
                   OverallSummary
           FROM t tl),
     ttt AS
        (    SELECT LEVEL lvl,
                    REGEXP_SUBSTR (tt.OverallSummary,
                                   '[^,]+',
                                   1,
                                   LEVEL)
                       LETTER
               FROM tt
         CONNECT BY LEVEL <= REGEXP_COUNT (tt.OverallSummary, ',') + 1)
SELECT listagg (letter, '||') WITHIN GROUP (ORDER BY lvl) str
  FROM (SELECT lvl,
               ROW_NUMBER () OVER (PARTITION BY letter ORDER BY 1) rnk,
               letter
          FROM ttt)
WHERE rnk = 1
Output:
STR
T111||T222||T444||T555
Cheers,
Manik.