Question

I’m trying to get the first category (level zero, no parents) from a child category (which might be any level) with just one query with MySQL. Is that possible?

Here’s an example DB structure :

Table categories

    id (INT 11)
    parent (INT 11, zero if it has no parent)
    name

edit: Would MPTT be a easier solution to the problem?

Answer 1

It is impossible to scan infinite levels with only one query but if you are sure your categoies tree doesn’t go deeper than a certain number of levels you can use this trick, this is for 4 levels:

SELECT COALESCE(c4.parent, c3.parent, c2.parent, c1.parent)
 FROM categories AS c1
 LEFT JOIN categories AS c2 ON( c1.parent = c2.id )
 LEFT JOIN categories AS c3 ON( c2.parent = c3.id )
 LEFT JOIN categories AS c4 ON( c3.parent = c4.id )
 WHERE c1.id = {someID}