php mysql query get value of a table with two different ID

Question

I have this table names MyLevels.

 id  | level | ParentLevelId
 ---------------------
 1   | basic | 1
 2   | silver| 1
 3   | gold  | 2
 4   | stone | 3
 5   | wood  | 2

on this table every level has a parent level. For example the "gold" level parent id is 2. It's mean the parent level is "silver" .
So I need a query to get the below in a html table: Parent level comes from ParentLevelId .

level  | parent level | distance From Basic
-------------------------------------------
basic  | basic        | 0
silver | basic        | 1
gold   | silver       | 2

The distance from basic reference to the number that each level is far from basic level.
For example the wood level id is 5 and 5 - 1 = 4 . which means the it's 4 level far from basic level.
This is the only code I have:

$conn->prepare('SELECT id, level, ParentLevelId FROM MyLevels');

Any help appreciated.

Thanks

Answer 1

You can join the table with itself to get the name of the parent level from the parent ID. Join it again to get the ID of the basic level, so you can subtract the ID from that.

SELECT m2.level, m1.level AS parentLevel, m2.id - m3.id AS distanceFromBasic
FROM MyLevels AS m1
JOIN MyLevels AS m2 ON m1.id = m2.parentLevelId
CROSS JOIN MyLevels AS m3
WHERE m3.level = 'basic'

DEMO

Answer 2

SELECT
    ml1.level,
    (
        SELECT
            ml2.level
        FROM
            MyLevels AS ml2
        WHERE
            ml2.id = ml1.ParentLevelId
    ) AS parentLevel,
    (
        SELECT
            ml1.id - ml2.id
        FROM
            MyLevels AS ml2
        WHERE
            ml2.level = 'basic'
    ) AS distanceFromBasic
FROM
    MyLevels AS ml1;

Just keep in mind this only works if that column is the primary key or is unique and that column is being used as the parentID.