how to match an integer with varchar containing digits separated by commas in oracle - oracle

Question

I am facing a strange scenario where I need to match an integer with varchar containing digits separated by commas in oracle
Example:
Table t1:
id integer
key integer
Table t2
id integer,
keys varchar2
T1 values are:
1,111
2,201
3,301
T2 values are:
1, "111,301"
2, "111,201"
3, "201,301"
PROBLEM: Is there any way I can match or regular_expression match with key of T1 with keys of T2?

Answer 1

you can do a regular join without regex for this:
select *
from t1
inner join t2
on ','||t2.keys||',' like '%,'||to_char(t1.key)||',%';
eg:
SQL> create table t1(id, key)
2 as
3 select 1, 111 from dual union all
4 select 2, 201 from dual union all
5 select 3, 301 from dual;
Table created.
SQL> create table t2(id, keys)
2 as
3 select 1, '111,301' from dual union all
4 select 2, '111,201' from dual union all
5 select 3, '201,301' from dual;
Table created.
SQL> select *
2 from t1
3 inner join t2
4 on ','||t2.keys||',' like '%,'||to_char(t1.key)||',%';
ID KEY ID KEYS
---------- ---------- ---------- -------
1 111 1 111,301
1 111 2 111,201
2 201 2 111,201
2 201 3 201,301
3 301 1 111,301
3 301 3 201,301
6 rows selected.
It's not regex, just concatenation. For example lets say we wanted to compare
KEY KEYS
111 111,301
we could say
where keys like '%'||key||'%'
i.e. expanded, this is
where '111,301' like '%111%'
which matches fine. But I added some commas there too. ie I did this:
where ',111,301,' like '%,111,%'
Why? imagine instead you had this data:
KEY KEYS
111 1111,301
If we did the simple join:
where '1111,301' like '%111%'
it would incorrectly match. By injecting leading and trailing commas on both sides:
where ',1111,301,' like '%,111,%'
is no longer erroneously matches, as ,1111, isn't like ,111,.