Determine whether a specific entry has any children in a hierarchical database

Question

I'm working on a recursive query for a hierarchal table in psql. While I'm able to produce an ordered, hierarchal list, I cannot figure out how to determine whether a parent has any children.

My code at the moment:

WITH RECURSIVE q AS (
  SELECT h, 1 AS level, ARRAY[ordering] AS ordered_path, ARRAY[id] AS breadcrumb
  FROM report h
  WHERE parent IS NULL
  UNION ALL
  SELECT hi, q.level + 1 AS level, ordered_path || ordering, breadcrumb || id FROM q
  JOIN report hi ON hi.parent = (q.h).id )
SELECT (q.h).id, (q.h).parent, (q.h).name, array_to_json(breadcrumb) AS breadcrumbs,
  row_number() OVER (order by ordered_path) AS flat_order
FROM q
ORDER BY ordered_path

Which produces the following table:

id  | parent |           name        | ordering |    trail     | rownum 
----+--------+-----------------------+----------+--------------+--------
  1 |        | Entry 1               |        1 | [1]          |      1
  2 |      1 | Entry 2               |        1 | [1,2]        |      2
 15 |      2 | Entry 3               |        1 | [1,2,15]     |      3
159 |      2 | Entry 4               |        2 | [1,2,159]    |      4
 16 |      2 | Entry 5               |        3 | [1,2,16]     |      5

Essentially, I'd like a column that shows if a specific entry has any children. In this example, Entry 5 has no children.

The format of the original table is:

id  |                        name              |  type   | parent | ordering 
-----+-----------------------------------------+---------+--------+----------
186 | Entry 1                                  | page    |    172 |       23
154 | Entry 2                                  | page    |     63 |        3
169 | Entry 3                                  | page    |    163 |        3

Thanks!

Answer 1

You could use a correlated subquery as an extra field:

exists (select 1 from report where parent = q.id) as has_children

It's not necessarily the most efficient — though tbh, given the query, I'm can't think of anything better off the top of my head. But it'll work.

Answer 2

sql below fill find the child and will count you can change how you want the output by using case statements I tested the code, seems to be working

select x.Col1, count(y.Col1) as child from Table1 x
inner join Table2 y on x.Col1 = y.Col1
group by x.Col1