Question

I have a tree representation in mysql table based on id, depth, parent_id and path. Every root record within this table has a depth of 0, parent_id != null and path representation based on hex value of ID padded left with 0.

Every element of the tree is constructed by specifying depth = parent.depth + 1, path = parent.path + hex(id), parent_id = parent.id (pseudo code) for example:

id    path            depth    parent_id    assigned_user_id
------------------------------------------------------------
1     001             0        NULL         NULL
2     002             0        NULL         1
3     001003          1        1            2
4     002004          1        2            1
5     001003005       2        3            2
6     001003005006    3        5            2
7     002004007       2        4            1
8     002004008       2        4            2
9     002004009       2        4            2
10    00200400800A    3        8            2

and so on…
The problem is how to get the records for specific user id limited to the shortest path in the same branch. For example for assigned_user_id = 2 retrive:

id    path            depth    parent_id    assigned_user_id
------------------------------------------------------------
3     001003          1        1            2
8     002004008       2        4            2
9     002004009       2        4            2

Instead of:

id    path            depth    parent_id    assigned_user_id
------------------------------------------------------------
3     001003          1        1            2
5     001003005       2        3            2
6     001003005006    3        5            2
8     002004008       2        4            2
9     002004009       2        4            2
10    00200400800A    3        8            2

Answer 1

SELECT t1.*
FROM atable t1
  LEFT JOIN atable t2
    ON t2.assigned_user_id = t1.assigned_user_id AND
       t2.path = LEFT(t1.path, CHAR_LENGTH(t2.path)) AND
       t2.id <> t1.id
WHERE t1.assigned_user_id = 2
  AND t2.id IS NULL