Remove duplicates from comma separated list with regexp

Question

I have

contract, clause 1, Subsection 1.1, contract, clause 1, Subsection 1.2,
paragraph (a), contract, clause 1, Subsection 1.2, paragraph (b), contract, 
clause 2 

and I want to get

contract, clause 1, Subsection 1.1, Subsection 1.2, paragraph (a), paragraph 
(b), clause 2

I've found that regexp can do this but I can not find which string to use to do it

Please help..

Answer 1

Based on this link to split a comma separated value into rows, I splitted the string into rows, kept the position of the first occurence, made a distinct a reaggregated the values

with test_string as ( 
select 1 as id,
 'contract, clause 1, Subsection 1.1, contract, clause 1, Subsection 1.2, paragraph (a), contract, clause 1, Subsection 1.2, paragraph (b), contract, clause 2' val 
from dual)
select id, listagg(word,', ') WITHIN GROUP (order by position) FROM (
select distinct id, first_value(position) over ( partition by word order by position ) position, word from (
select 
  distinct t.id,
  levels.column_value as position,
  trim(regexp_substr(t.val, '[^,]+', 1, levels.column_value))  as word
from 
  test_string t,
  table(cast(multiset(select level from dual connect by  level <= length (regexp_replace(t.val, '[^,]+'))  + 1) as sys.OdciNumberList)) levels
  )
) GROUP BY id

And if you are not interested in keeping the order

with test_string as ( 
select 1 as id,
 'contract, clause 1, Subsection 1.1, contract, clause 1, Subsection 1.2, paragraph (a), contract, clause 1, Subsection 1.2, paragraph (b), contract, clause 2' val 
from dual)
select id, listagg(word,', ') WITHIN GROUP (order by 1) FROM (
select 
  distinct t.id,
  trim(regexp_substr(t.val, '[^,]+', 1, levels.column_value))  as word
from 
  test_string t,
  table(cast(multiset(select level from dual connect by  level <= length (regexp_replace(t.val, '[^,]+'))  + 1) as sys.OdciNumberList)) levels
) GROUP BY id