Combining Arrays With PHP mySQL

<?php
include('connect.inc');
$db=public_db_connect();

// names from table #1
$command = "SELECT * FROM table_sort ";
$result = mysqli_query($db, $command);

while($row = mysqli_fetch_assoc($result)){

    $firstname = $row['firstname'];
    $lastname =  $row['lastname'];
    $array_list[] = $firstname."-".$lastname;
}

// names from table #2
$command2 = "SELECT * FROM table_sort2 ";
$result2 = mysqli_query($db, $command2);

while($row = mysqli_fetch_assoc($result2)){

    $firstname = $row['firstname'];
    $lastname =  $row['lastname'];
    $array_list[] = $firstname."-".$lastname;
}

// names from table #3
$command3 = "SELECT * FROM table_sort3 ";
$result3 = mysqli_query($db, $command3);
while($row = mysqli_fetch_assoc($result3)){

    $firstname = $row['firstname'];
    $lastname =  $row['lastname'];
    $array_list[] = $firstname."-".$lastname;
}

print_r($array_list);