PHP foreachで配列を削除する方法

Array
(
    [0] => Array
        (
            [uid] => 1
            [tid] => 0
            [username] => 123
            [truename] => 3333
            [groupid] => 1
        )
    [1] => Array
        (
            [uid] => 2
            [tid] => 0
            [username] => 321
            [truename] => 5
            [groupid] => 1
        )
    [2] => Array
        (
            [uid] => 4
            [tid] => 0
            [username] => 456
            [truename] => 5
            [groupid] => 2
        )

foreach($db as $v){  
    if($v['groupid'] == 1){
        unset($db[$v['groupid']]);
    }
｝

foreach($db as $k=>$v){  

    if($v['groupid'] == 1){        unset($db[$k]);
    }
｝