$sql="select * from a";
$result=$db->query($sql);

while($row=mysql_fetch_array($result))
{
    $arr["id"][]=$row["id"];
    $arr["no"][]=$row["no"];
    $arr["name"][]=$row["name"];
    
}

$sql2="select * from b";
$result2=$db->query($sql2);
while($row=mysql_fetch_array($result2))
{
    $arr2["id"][]=$row["id"];
    $arr2["address"][]=$row["address"];
}
function array_diff_rewrite($array1, $array2){
    //遍历$content中的key
    foreach($array1 as $k=>$v)
    {
        //判断array2数组中是否有与array1中相同的key,不存在则赋予
       if(!isset($array2[$k]))
       {
             $array2[$k]=$array1[$k];
       }
    }
    return $array2;
}
$arr3=array_diff_rewrite($arr,$arr2);
//print_r($arr3);
function insert($array1,$array2)
{    
foreach ($array1 as $k=>$v)
{
    if(!isset($array2[$k]))
            {
                $sql4="alter table b add $k varchar(200)";
            }
}
echo $sql4;
}

insert($arr3, $arr2);