Query to one parent record from multiple child record

1

Hi, Thanks in advance,I need help in creating SQL query to generate report to get one parent account for multiple child record( db - postgres db ).

example below with below rules

  1. For each "Id" consider lowest "sub_id" as parent_id and other as child_id
  2. The parent_id shoul be same for all child_id
    I.e. no child_id should have multiple parent_id
  3. The parent_id and child_id can't be same

Id sub_id
1 a11
1 a12
2 a13
2 a16
2 a17
2 a14
3 a31
4 a32
4 a33
4 a35

Final result
Parent_id child_id
a11 a12
a13 a14
a13 a16
a13 a17
a32 a33
a32 a35