如何从php中的树状数据结构中获取最后一级元素？

Question

My recursive function returns all the children of menu but I want to have just the last children of array, here is my code:

function test($pid){
    $arr = array();
    $sql = "SELECT * FROM wp_term_taxonomy WHERE parent=$pid && taxonomy='product_cat'";
    $result = mysqli_query($GLOBALS['conn'], $sql);

    if (mysqli_num_rows($result) > 0) {
        while ($row = mysqli_fetch_assoc($result)) {
            $term_taxonomy_id = $row['term_taxonomy_id'];   
            $arr[$row['term_taxonomy_id']] = test($row['term_taxonomy_id']);
        }
    }
    return $arr;
}   

Current output:

{"26":{"194":[],"195":[],"196":[],"197":[],"198":[],"199":[],"200":[]},"30":{"201":[],"202":[],"203":[],"204":[],"205":[],"206":[],"207":[]},"32":{"217":[],"218":[],"219":[],"220":[],"221":[],"222":[],"223":[],"224":[],"225":[]},"35":{"208":[],"209":[],"210":[],"211":[],"212":[],"213":[],"214":[],"215":[],"216":[]},"38":{"226":[],"227":[],"228":[],"229":[],"230":[],"231":[],"232":[],"233":[],"234":[],"235":[],"236":[],"237":[]},"41":{"238":[],"239":[],"240":[]},"43":{"241":[],"242":[],"243":[],"244":[],"245":[],"246":[],"247":[]},"45":{"248":[],"249":[],"250":[],"251":[],"252":[],"253":[],"254":[],"255":[],"256":[]},"47":{"257":[]}}

Expected output:

{"194","195","196","197","198","199","200","201,"202","203","204","205","206","207","217","218","219","220","221","222","223","224","225","208","209","210","211","212","213","214","215","216","226","227","228","229","230","231","232","233","234","235","236","237","238","239","240","241","242","243","244","245","246","247","248","249","250","251","252","253","254","255","256","257"}

Answer 1

Your code is pretty close - all you need to do is return stop condition to the function (no children in your case) and if not continue with the recursive calls.

You can just add pid in case he has no children and if he has just merge all his children:

function getLeafs($pid){
    $sql = "SELECT * FROM wp_term_taxonomy WHERE parent=$pid && taxonomy='product_cat'";
    $result = mysqli_query($GLOBALS['conn'], $sql);

    if (mysqli_num_rows($result) == 0) {
        return array($pid); // no children for this pid
    } else {
        $leafs = array();
        while ($row = mysqli_fetch_assoc($result)) {
            $leafs = array_merge($leafs, getLeafs($row['term_taxonomy_id']));
        }
        return $leafs;
    }
}