在sql select语句中生成数字

Question

I have a query that returns some parent records and child records. I would like to return for each child records a unique id by increment. So if i have a record with 3 childs and 1 with 2 childs would like to return.

     Parent/Child |  Parent_id | Child_id
1.   Parent record,  Parent_id,   0
2.   child_record,   Parent_Id,   1
3.   child_record,   Parent_Id,   2
4.   child_record,   Parent_Id,   3
5.   Parent record,  Parent_id,   0
6.   child_record,   Parent_Id,   1
7.   child_record,   Parent_Id,   2

Any ideas of how to generate the child_id from 1 and increment by 1 and then reset again for next batch of child records?

Answer 1

This query produces the child numbering contingent to their parent id:

select id_pk  -- pk; defines global sort order
     , p_c    -- node type ('parent', 'child')
     , p_id   -- parent id
     , row_number() over ( partition by p_id order by id_pk ) - 1 c_id
              -- synthetic child id. 
  from test_pc
     ;

Adjust the sorting criterion in the order by clause as needed.

Example: (order among children does not matter, just a unique local id is needed)

     , row_number() over ( partition by p_id order by p_id, p_c desc ) - 1 c_id