If you're using 11gR2 you can use RCTE:
with Idata as
(SELECT 1 Rn ,'id:a,val:b,desc:c' data FROM Dual
UNION ALL
SELECT 2 Rn ,'id:a2,val:b2,desc:c2' data FROM Dual
UNION ALL
SELECT 3 Rn ,'id:a3,val:b3,desc:c3' data FROM Dual),
rcte(rn, txt, token, i) as
(
select rn, data, Regexp_Substr(data, '[^,]+', 1, 1), 2
from Idata
union all
select rn, txt, Regexp_Substr(txt, '[^,]+', 1, i), i+1
from rcte
where Regexp_Substr(txt, '[^,]+', 1, i) IS NOT null
)
select rn, token
from rcte
order by rn;
If not, and adding DISTINCT is to heavy, then you can try a different approach such as using a pipelined function-
create or replace type t is object(token varchar2(100));
/
create or replace type t_tab as table of t;
/
create or replace function split_string(str varchar2, del in varchar2) return t_tab
pipelined is
token varchar2(4000);
str_t varchar2(4000) ;
v_del_i number;
begin
str_t := str;
while str_t is not null loop
v_del_i := instr(str_t, del, 1, 1);
if v_del_i = 0 then
token := str_t;
str_t := '';
else
token := substr(str_t, 1, v_del_i - 1);
str_t := substr(str_t, v_del_i + 1);
end if;
pipe row(t(token));
end loop;
return;
end split_string;
/
Now the query could look like this:
select t.token, Idata.rn
from (SELECT 1 Rn ,'id:a,val:b,desc:c' data FROM Dual
UNION ALL
SELECT 2 Rn ,'id:a2,val:b2,desc:c2' data FROM Dual
UNION ALL
SELECT 3 Rn ,'id:a3,val:b3,desc:c3' data FROM Dual) Idata ,
table(split_string(Idata.data, ',')) t