Question

I’m trying to remember what the SQL solution is for this type of problem. Let’s say I have the following tables:

tagged_nodes:

1. nid – Node id. Foreign key.
2. tid – Tag id. Foreign key.
3. tnid – Primary key (irrelevant to the problem at hand).

nodes:

1. nid – Node id. Primary key.
2. … – Other columns are irrelevant.

Assuming I have a set of tag ids (tid), I want to return the set of associated nodes (intersection). How do I do this?

Answer 1

So here’s what I’ve come up with:

$this->Sql = 'SELECT DISTINCT * FROM `nodes` `n`
    JOIN `tagged_nodes` `t` ON t.nid=n.nid';

 $i=0;
foreach( $tagids as $tagid ) {
     $t = 't' . $i++;
    $this->Sql .= ' INNER JOIN `tagged_nodes` `'.$t.'` ON '
        .$t'.tid=t.tid WHERE '.$t.'.tid='.$tagid;
}

It’s in PHP since I need it to be dynamic, but it would basically be the following if I needed, say, only 2 tags (animals, pets).

SELECT * FROM nodes n JOIN tagged_nodes t ON t.nid=n.nid
INNER JOIN tagged_nodes t1 ON t1.tid=t.tid WHERE t1.tid='animals'
INNER JOIN tagged_nodes t2 ON t2.tid=t.tid WHERE t2.tid='pets'

Am I on the right track?