Question

I have a SQL table with the following structure.

id   - int
par  - int (relational to id)
name - varchar

Column par contains references to id or NULL if no reference, this table is meant to build an hierarchical tree.

Then, given the data:

id par  name

1  NULL John
2  NULL Mario
3  1    George
4  3    Alfred
5  4    Nicole
6  2    Margaret

I want to retrieve a hierarchical tree, up to the last parent, from a given single id.

Example, I want to know the tree from Nicole to the last parent. So the query result will be:

id par  name

5  4    Nicole
4  3    Alfred
3  1    George
1  NULL John

I would normally do this with a SQL query repeating over and over and building the tree server side but I do not want that now.

Is there any way to achieve this with a single SQL query?
I need this for either MySQL or PgSQL.

And I want to know also, if possible, is it also widely supported? In which versions of either MySQL or PgSQL can I expect support?

Answer 1

It is possible with a single query in Postgres using a recursive common table expression. This is not possible in MySQL as it is one of the few database to not support recursive CTEs.

It would look something like this (not tested)

WITH RECURSIVE tree (id, par, name) AS (
    SELECT id, par, name 
    FROM the_table
    WHERE name = 'Nicole'

    UNION ALL

    SELECT id, par, name 
    FROM the_table tt
      JOIN tree tr ON tr.id = tt.par
)
SELECT *
FROM tree