Oracle : SQL to replace items in a string with items of another string - sql

Question

I have a column "col1" value like : 'a,b,x,y,z' (ordered string)
Another column "col2" is like : 'a,x' or 'b,y,z' (ordered string)
All the string values in "col2" are generated by a subquery. So it is not constant.
But, the value in "col1" is constant. That is col1='a,b,x,y,z'
create table test (col1 varchar2(20), col2 varchar2(10));
insert into test values ('a,b,x,y,z','a,x');
insert into test values ('a,b,x,y,z','b,y,z');
Need help with the replacing in one sql.
Need help to replace the elements on "col1" with "col2".
For example,
when col2='a,x', the result should be : 'b,y,z'
when col2='b,y,z', the result should be : 'a,x'

Answer 1

Here is a fun way to do this:
select col1, col2,
ltrim(regexp_replace(translate(replace(col1,','),','||replace(col2,','),',')
,'(.)',',\1'),',') as col3
from test;
That is: (reading the function calls as they are executed, from inside out)
Remove the commas from both strings
Use TRANSLATE() to remove the characters of the second string from the first string
Use REGEXP_REPLACE to add commas before each character of the remaining string
Trim the leading comma

Answer 2

Here's one option; I included the ID column to make it simpler. I hope that a column similar to it exists in your real case.
The idea is:
split each column (col1, col2) to rows
CTE one represents col1's rows
CTE two represents col2's rows
using the MINUS set operator, subtract those two sets of rows
using LISTAGG, aggregate the result
SQL> select * From test;
ID COL1 COL2
---------- -------------------- ----------
1 a,b,x,y,z a,x
2 a,b,x,y,z b,y,z
SQL> with
2 one as
3 (select id, regexp_substr(col1, '[^,]+', 1, column_value) col
4 from test,
5 table(cast(multiset(select level from dual
6 connect by level <= regexp_count(col1, ',') + 1
7 ) as sys.odcinumberlist))
8 ),
9 two as
10 (select id, regexp_substr(col2, '[^,]+', 1, column_value) col
11 from test,
12 table(cast(multiset(select level from dual
13 connect by level <= regexp_count(col2, ',') + 1
14 ) as sys.odcinumberlist))
15 ),
16 t_minus as
17 (select id, col from one
18 minus
19 select id, col from two
20 )
21 select id, listagg(col, ',') within group (order by col) result
22 From t_minus
23 group by id;
ID RESULT
---------- --------------------
1 b,y,z
2 a,x
SQL>