Getting all parent rows in one SQL query

Question

I have a simple MySQL table thats contains a list of categories, level is determined by parent_id:

id  name    parent_id
---------------------------
1   Home         


        

Answer 1

In addition to the above solutions:

post
-----
id
title
author

author
------
id
parent_id
name


[post]

id  | title | author |  
----------------------
1   | abc   | 3      |


[author]

| id    | parent_id | name  |   
|---------------------------|
| 1     | 0         | u1    |
| 2     | 1         | u2    |
| 3     | 2         | u3    |
| 4     | 0         | u4    |

an author including parents can have an access to the post.

I want to check whether author has an access to the post.

Solution:

give the post author's id and return all its authors and author's parents

SELECT T2.id, T2.username 
FROM (
    SELECT @r AS _id, 
        (SELECT @r := parent_id FROM users WHERE id = _id) AS parent_id,
        @l := @l + 1
    FROM
        (SELECT @r := 2, @l := 0) vars, 
        users h     
    WHERE @r <> 0) T1 JOIN users T2 
ON T1._id = T2.id;

@r := 2 => assigning value to @r variable.