php mysql get all parents

Question

i'm trying to get all parents of children. I have a simple query select from sections where sectionID = 6 The database structure is very simple

sectionID parent
1     0
2     1
3     1
4     2
5     4
6     5

Now I'm trying to get all parents from sectionID 6, the result should be a string 0/2/4/5/6. children might not have a lot of parents, it might have only one so the result should be different. ie 5/6.. I hope you understand what I'm trying to do. I have tried couple recursive functions which i've found on the internet, but I really suck at this and was wondering if anyone could help me to get on the right track. PS I'm using php and mysql

Answer 1

Well, as far as I can see you have two choices, both well known.

1) You make a recursive function, just the ones you have been trying. There are tons of them around and i won't put him in here.

2) By far my favourite, this is the Database pattern most modern ORM use, it's called nested set model.

Basically you create a few more columns on the table, it should look like this one:

CREATE TABLE nested_category (
        category_id INT AUTO_INCREMENT PRIMARY KEY,
        name VARCHAR(20) NOT NULL,
        lft INT NOT NULL,
        rgt INT NOT NULL
);

INSERT INTO nested_category VALUES(1,'ELECTRONICS',1,20),(2,'TELEVISIONS',2,9),(3,'TUBE',3,4),
 (4,'LCD',5,6),(5,'PLASMA',7,8),(6,'PORTABLE ELECTRONICS',10,19),(7,'MP3 PLAYERS',11,14),(8,'FLASH',12,13),
 (9,'CD PLAYERS',15,16),(10,'2 WAY RADIOS',17,18);

SELECT * FROM nested_category ORDER BY category_id;

+-------------+----------------------+-----+-----+
| category_id | name                 | lft | rgt |
+-------------+----------------------+-----+-----+
|           1 | ELECTRONICS          |   1 |  20 |
|           2 | TELEVISIONS          |   2 |   9 |
|           3 | TUBE                 |   3 |   4 |
|           4 | LCD                  |   5 |   6 |
|           5 | PLASMA               |   7 |   8 |
|           6 | PORTABLE ELECTRONICS |  10 |  19 |
|           7 | MP3 PLAYERS          |  11 |  14 |
|           8 | FLASH                |  12 |  13 |
|           9 | CD PLAYERS           |  15 |  16 |
|          10 | 2 WAY RADIOS         |  17 |  18 |
+-------------+----------------------+-----+-----+

If you notice there is no parent_id column. To be able to search for it's childrens for, let's say row 5 the query will be like:

Select * from nested_category where left > 7 and left < 8 order by left asc, which will bring no results.

For row number 1 the result however will bring the entire tree.

I have no php script for autocreating those columns on this computer, but there are plenty around. Im afraid they are also recursive.

You my find lots of info around searching for "nested set model", like this or theorical exaplanations of the model like this one

AND THIS IS A WAY DUPLICATED QUESTION (i can not put it as duplicated)

Some other answers:

• This guys do it all in mysql

• Some more answers here

You should reread the forum rules before posting, look for already asked questions.

Hope it helps.

Answer 2

I'm not going to write all the code, but this idea should work if I understand your database shema correctly.

section = 6
result = ""
while section != ""
    select parent where sectionID = section
    result += parent
    section = parent
return result