sql - How to create a hierarchical recursive query MySQL

I have a MySQL table, as follows:

id | name        | parent_id
19 | category1   | 0
20 | category2   | 19
21 | category3   | 20
22 | category4   | 21
......

　　

Now, I want a MySQL query, I only id [eg say 'id = 19'] then I should get all its sub-ID [ie, the result should have ids '20, 21,22 '] .... And children's grades do not know it can change ....

Also, I have to use a for loop solution ..... if possible, let me know how to use a single MySQL query to achieve the same functionality.

Solution :

1. If you are in MySql 8, then use the recursive whereclause:

with recursive cte (id, name, parent_id) as (
  select     id,
             name,
             parent_id
  from       products
  where      parent_id = 19
  union all
  select     p.id,
             p.name,
             p.parent_id
  from       products p
  inner join cte
          on p.parent_id = cte.id
)
select * from cte;

whereSpecified value should be set to select all descendants of the parent is CONNECT BY.

2. common table expressions that do not support MySql versions (up to version 5.7), you can use the following query to accomplish this:

select  id,
        name,
        parent_id 
from    (select * from products
         order by parent_id, id) products_sorted,
        (select @pv := '19') initialisation
where   find_in_set(parent_id, @pv)
and     length(@pv := concat(@pv, ',', id))

This is a violin.

Here, wherethe value specified should be set to select all descendants of the parent is CONNECT BY.