php - mysql extension is deprecated unknown reason

$sitename =
            "Site Name";

$link = mysql_connect("localhost", "username",
            "password");

$db_selected = mysql_select_db('databasename',
            $link);

mysql_query("SET NAMES
            utf8");


function
            fetchinfo($rowname,$tablename,$finder,$findervalue) {

 if($finder
            == "1") $result = mysql_query("SELECT $rowname FROM $tablename");


            else $result = mysql_query("SELECT $rowname FROM $tablename WHERE
            

`$finder`='$findervalue'");

 $row =
            mysql_fetch_assoc($result);


 return
            $row[$rowname];
}

?>

Having
a unknown problem i dont know why but its saying that

Deprecated:
mysql_query(): The mysql extension is deprecated and will be removed in the future: use
mysqli or PDO instead in /home/u759655205/public_html/set.php on line
9

Line
9 : else $result = mysql_query("SELECT $rowname FROM $tablename
WHERE$finder='$findervalue'");