Question

I have a table like this-

id  name        ordering    catid 
1   parent1         1         0
2   parent2         2         0
3   parent3         3         0
4   child11         1         1
5   child12         2         1
6   child21         1         2
7   child22         2         2
8   child31         1         3
9   child32         2         3

I am trying to get the result like below-

id  name        ordering    catid 
1   parent1         1         0
4   child11         1         1
5   child12         2         1
2   parent2         2         0
6   child21         1         2
7   child22         2         2
3   parent3         3         0
8   child31         1         3
9   child32         2         3

I want to order the first parent(catid=0) than its child than second parent and its child.
Is this possible to achieve desire result with these column.I tried join but not succeeded.
Surely I am not doing it correctly.
This is what I have tried-

SELECT a.*,c.name AS category_title FROM table AS a 
LEFT JOIN table AS c ON c.id = a.catid 
ORDER BY c.ordering asc, a.ordering asc

Answer 1

This query would do a SELF JOIN on the same table, by joining the records from the first table with the corresponding parent records. The column parentId would contain the parent Id of the record if the parent existed, otherwise the ID of the record itself. The results are then ordered by parentId and then by the ID so that the parent always appears at the top in a given group of parent and its children.

SELECT
    m.id, 
    m.name, 
    m.catid, 
    m.ordering, 
    p.ordering,
    case 
        WHEN p.ordering IS NULL THEN m.ordering * 10
        ELSE m.ordering + p.ordering * 10
    END AS parentId
FROM
    MyTable m
    LEFT JOIN MyTable p
    ON m.catid = p.id
ORDER BY parentId

The result is as follows:

1   parent1 0   1       10
4   child11 1   1   1   11
5   child12 1   2   1   12
2   parent2 0   2       20
6   child21 2   1   2   21
7   child22 2   2   2   22
3   parent3 0   3       30
8   child31 3   1   3   31
9   child32 3   2   3   32