MYSQL返回父和子

Question

Ok so I have a table called categories that looks like this:

id       name      parent_id
1        camera    null
2        computer  null
3        digital   1
4        gps       null
5        laptop    2

I want to be able to return computer -> laptop or camera -> digital when I query id = 3 or 5.

Any ideas?

Answer 1

Try Nestedsets for those Structurs. It has a very good performance for selecting, but a bad performance for writing. So if you have much more Selects, as Insert or Updates (Structure Updates) on your Table its a good choice to use nested sets.

Breadcrumps with Nested Sets to get Category 1 -> SubCategory -> SubCategory

Answer 2

if it's fixed column count of results set

select p.name, c.name
mytable c, mytable p
where c.parent_id = p.id
and c.id in (3,5)

Answer 3

What you are trying to use is an anti-pattern. If you continue using it you may encoutner some problems when you will want to select entire trees of subcategories. Look at take's answer for proper pattern.

Answer 4

select t2.name + "->" + t1.name 
from categories t1
inner join t2 on t1.id = t2.parent_id
where t1.id in (3, 5)

Answer 5

If you only have one level of parent - child references:

SELECT IF(p.name IS NOT NULL, p.name + " -> " + a.name, a.name) AS name
FROM categories a
LEFT JOIN categories p ON a.parent_id = p.id

Answer 6

Use a self left join :

select a.name, b.name as parent_name from categories a left join categories b on a.parent_id = b.id where a.id in (3,5);

Above query is valid for getting a one level of parent. If you want to traverse through the whole lineage please refer the following link. They have listed down few standard ways of traversing tree :

http://jan.kneschke.de/projects/mysql/sp/