Gathering information from parent record to child records

I have a table which has ids as m_id and child_id, both are inter-connected as follows :

m_id	child_id	op_status
1	null	finish
2	null	finish
3	null	finish
4	1	on-going

In this example, m_id => 1 has two op_status as "finish" and "on-going". Another table is also joined with m_id for this table as follows :

c_id	m_id	make	model	status
100	1	Acer	Aspire	1
101	1	Acer	Aspire	1

Then I need to get the following output for the using these 02 tables as follows :

m_id	child_id	make	model	op_status
1	null	Acer	Aspire	finish
2	null	Acer	Aspire	finish
3	null	Acer	Aspire	finish
4	1	Acer	Aspire	on-going

I used the following query to do that.

SELECT T1.m_id, T1.child_id, T2.make, T2.model, T1.op_status
FROM parent T1, child T2
WHERE T1.m_id = T2.m_id

But didn't get the disired above output and returns the result set as follows :

m_id	child_id	make	model	op_status
1	null	Acer	Aspire	finish

What might be missed by myself ? Can help anyone on this ?

Output as per Chiara Tumminelli's suggestion.

m_id	child_id	make	model	op_status
1	NULL	Acer	Aspire	finish
2	NULL	NULL	NULL	finish
3	NULL	NULL	NULL	finish
4	1	NULL	NULL	on-going

Solution

Assuming that your consecutive m_id values are associated to the same instance when child_id values are all null (before another non-null value), you can carry out this task with two joins to match:

table1 parent m_id with table1 child m_id
table1 child m_id with table2 m_id

SELECT t11.m_id, 
       t11.child_id,
       t2.make,
       t2.model,
       t11.op_status
FROM       tab1 t11 
INNER JOIN tab1 t12
        ON t11.m_id >= t12.child_id
INNER JOIN (SELECT DISTINCT m_id, make, model FROM tab2) t2
        ON t12.child_id = t2.m_id

Output:

m_id	child_id	op_status	make	model
1	null	finish	Acer	Aspire
2	null	finish	Acer	Aspire
3	null	finish	Acer	Aspire
4	1	on-going	Acer	Aspire

Check the demo here.

If you have a more complex gaps-and-islands problem, you may need to regenerate your partitions (m_id unique values) by:

create a flag that indicates when to change partition
compute a running sum over your flag
gather the corresponding values of make, model, for each of your partitions

WITH cte AS (
    SELECT t11.m_id, 
           t11.op_status,
           CASE WHEN t12.child_id IS NOT NULL 
                  OR LAG(t11.child_id) OVER(ORDER BY t11.m_id) IS NOT NULL
                THEN 1
           END AS change_part,
           t11.child_id,
           t2.make,
           t2.model
    FROM      tab1 t11
    LEFT JOIN tab1 t12
           ON t11.m_id = t12.child_id
    LEFT JOIN (SELECT DISTINCT m_id, make, model FROM tab2) t2
           ON t12.child_id = t2.m_id
), cte2 AS (
    SELECT m_id, 
           op_status, 
           child_id, 
           make, 
           model,
           SUM(change_part) OVER(ORDER BY m_id) AS parts
    FROM cte
)
SELECT m_id, 
       op_status, 
       child_id,
       MAX(make)     OVER(PARTITION BY parts) AS make,
       MAX(model)    OVER(PARTITION BY parts) AS model
FROM cte2
ORDER BY m_id

Check the demo here.