how to get a grand child from parent in php

Question

Hi all i need a help i need to display a grand child from parent id that means one id=2 has a child id=3 and child id=3 has a child id=4 (here child id=3 is parent id for child id=4).

below is my tables:

table object_data:
obj_id | type | title 
---    |------|------
3217   |crs   |it 
3221   |grp   |xyz 
3228   |tst   |test 

table object_reference:
ref_id | obj_id 
---    |---------
337    |3217       
338    |3221      
343    |3228 

table tree:
tree | child | parent 
---  |-------|------
1    |338    |337 
2    |343    |338 

from above three tables i need to display like id 3217 has id 3228 i need a query .i am able to write a query for only child id not for grand child .any one help to sort out this

Answer 1

This gives you the parent and grand child info:

SELECT
    a.`type` as `parent_type`,
    a.`title` as `parent_title`,
    g.`type` as `gchild_type`,
    g.`title` as `gchild_title`
FROM `object_data` a
JOIN `object_reference` b
    ON a.`obj_id` = b.`obj_id`
JOIN `tree` c
    ON b.`ref_id` = c.`parent`
JOIN `object_reference` d
    ON c.`child` = d.`ref_id`
JOIN `tree` e
    ON d.`ref_id` = e.`parent`
JOIN `object_reference` f
    ON e.`child` = f.`ref_id`
JOIN `object_data` g
    ON f.`obj_id` = g.`obj_id`

EDIT

This gives you the parent, child and grand child info:

SELECT
    a.`type` as `parent_type`,
    a.`title` as `parent_title`,
    g1.`type` as `child_type`,
    g1.`title` as `child_title`,
    g.`type` as `gchild_type`,
    g.`title` as `gchild_title`
FROM `object_data` a
JOIN `object_reference` b
    ON a.`obj_id` = b.`obj_id`
JOIN `tree` c
    ON b.`ref_id` = c.`parent`
JOIN `object_reference` d
    ON c.`child` = d.`ref_id`
JOIN `object_data` g1
    ON d.`obj_id` = g1.`obj_id`
JOIN `tree` e
    ON d.`ref_id` = e.`parent`
JOIN `object_reference` f
    ON e.`child` = f.`ref_id`
JOIN `object_data` g
    ON f.`obj_id` = g.`obj_id`

Answer 2

You can easily join the three tables by matching the right columns to each other:

SELECT tree.child
FROM object_data
JOIN object_reference ON object_data.obj_id = object_reference.obj_id
JOIN tree ON tree.parent = object_reference.ref_id
WHERE object_data.obj_id = 3217