Question

Consider the following:

Table - id, parentid

What I’d like to do, is I’d like to pull all the children (not only direct children, but all of them, i.e. children of children of children etc.) of a specific parent.

So let’s say the table contains the following row: (2, 1), (3, 1), (4, 2), (5, 4)

Then for parentid = 1, the table would return ids 2, 3, 4 AND 5.

Is this possible?

If not (and I guess it’s indeed not possible), what are my options?

I really don’t want to use dozens of queries…

P.S. I can’t change the database structure.

Also, as there might be hundreds of thousands of records in the table, I can pull them all and do the whole thing using PHP instead.

Answer 1

This might help:

$parentId = 1; // the parent id
$arrAllChild = Array(); // array that will store all children
while (true) {
    $arrChild = Array(); // array for storing children in this iteration
    $q = 'SELECT `id` FROM `table` WHERE `parentid` IN (' . $parentId . ')';
    $rs = mysql_query ($q);
    while ($r = mysql_fetch_assoc($rs)) {
        $arrChild[] = $r['id'];
        $arrAllChild[] = $r['id'];
    }
    if (empty($arrChild)) { // break if no more children found
        break;
    }
    $parentId = implode(',', $arrChild); // generate comma-separated string of all children and execute the query again
}
print_r($arrAllChild);

You may as well use recursion to do so but I think the above will need fewer iterations.

Hope it helps!

EDIT – I forgot to mention that you can as well implement the same logic in a MySQL stored procedure except that you cant use Arrays. The above example is implemented in PHP as you might have already guessed