Group concat all child ids against parent row using query in Mysql

Question

Having records in table as below, And we can add record as endless hierarchy

-----------------------------------------
| id | name                  | parent_id |
-----------------------------------------
| 1  | Income                | NULL      |
| 2  | Bank Account Interest | 1         |
| 3  | FD Interest           | 1         |
| 4  | Personal Account      | 2         |
| 5  | Salary Account        | 2         |
| 6  | Expense               | NULL      |
| 7  | Daily Need Expense    | 6         |
| 8  | Mobile Expense        | 6         |
| 9  | Vehicle Expense       | 6         |
| 10 | vehicle InsuranceRenew| 9         |
| 11 | Father FD             | 3         |
------------------------------------------ 

Need Output as below if parent_id is null,

------------------------------------------
| id | name                  | child_ids |
------------------------------------------
| 1  | Income                | 2,3,4,5,11|
| 2  | Expense               | 7,8,9,10  |
------------------------------------------

Need Output as below if parent_id = 2,

------------------------------------------
| id | name                  | child_ids |
------------------------------------------
| 2  | Bank Account Interest | 4,5,11    |
------------------------------------------

Answer 1

DB Fiddle: https://www.db-fiddle.com/f/6i2dwPvg4PqTfxyCTQZoho/0

And your query could look like

with recursive myCTE (root_id, id, parent_name, parent_id) as (
    # the most basic level, we need to remember the root id and name
    select id as root_id,
           id,
           name as parent_name,
           parent_id
    from myTable
    # you can control which output you need here or at the end (modifying the `from myCTE`
    where parent_id is null
    # or with that
    # where id = 2

    union all
  
    # combine that in recursive way
    select mC.root_id,
           mT.id,
           mC.parent_name,
           mT.parent_id
    from myTable mT
    inner join myCTE mC on mT.parent_id = mC.id
)
select root_id, parent_name, group_concat(id)
from myCTE
where id <> root_id
group by root_id, parent_name;

It uses the recursive CTE statements (see https://dev.mysql.com/doc/refman/8.0/en/with.html#common-table-expressions-recursive) which allows to gather such hierarchical rows together. At the end, the GROUP_CONCAT is used to combine together strings by groups.