紧急求助，关于mysql里的求和

Question

<?
        include "db_connect.php";
        $str="SELECT SUM(cost) FROM pgwr";
        $str1=mysql_query($str);
$row=mysql_fetch_array($str1);
echo $row[0];
        ?>

Answer 1

<?
        include "db_connect.php";
        $str="SELECT SUM(cost) as SUM FROM pgwr";
        $result=mysql_query($str);
        if($rst=mysql_fetch_object($result))
            echo $rst->SUM;
        ?>

Answer 2

<?
        include "db_connect.php";
        $str="SELECT SUM(cost) FROM pgwr";
        $str1=mysql_query($str);
/////////////这里少了取出数据的函数
        echo "$str1";
        ?>

Answer 3

<?
        include "db_connect.php";
        $str="SELECT SUM(cost) as ans FROM pgwr";
        $result=mysql_query($str);
        if($rst=mysql_fetch_object($result)){
            echo $rst["ans"];
           }
        ?>

Answer 4

<?
include "db_connedt.php";
$str="select sum(cost) as sumconst from pgwr";
$res = mysql_query($str, $dbh); 
$err = mysql_error(); 
if($err){ 
  echo "发生错误，请通知<a href=mailto:[email protected]>站长</a>"; 
} 
else
{
  $row = mysql_fetch_row($res); 
  echo "总数为: ".$row[0]; 
}
?>