Get All record when like each other join query

Question

I have one table registration

registration table
+------+------+
|ARIDNR|LIEFNR|
+------+------+
|1     |A     |
+------+------+
|2     |B     |
+------+------+
|3     |C     |
+------+------+

UserLike Table
+------+------+
|ARIDNR|LIEFNR|
+------+------+
|A     |B     |
+------+------+
|B     |A     |
+------+------+
|A     |C     |
+------+------+

I would like to select join query with userlike table get those value return true when both user like each other

Example

User A is like User B Also User B is Like User A

so I get return true in User B response

in this case User A is like User C but User C is not Like User A in this case return false

I want output like below

Result

{
“username”:B
“match”:true    
},
{
“username”:C
“match”:false   
}

Answer 1

Assuming now duplicates, you can do:

select least(ARIDNR, LIEFNR), greatest(ARIDNR, LIEFNR)
from userlike
group by least(ARIDNR, LIEFNR), greatest(ARIDNR, LIEFNR)
having count(*) = 2;

Or, more efficiently (with the right indexes) as:

select ul.*
from userlike ul
where ul.ARIDNR < ul.LIEFNR and
      exists (select 1
              from userlike ul2
              where ul2.ARIDNR = ul.LIEFNR and
                    ul2.LIEFNR = ul.ARIDNR
             );