Input fields into MySQL with PHP

<?

if (count($_POST)>0)
{
    $incoming = $_POST;

    $fields_with_content = 0;
    $empty_fields = 0;
    $sql = 'INSERT INTO entries SET ';
    $sep = '';
    foreach($incoming as $key=>$value)
    {
        echo "The input field <b>$key</b> contains the value '$value'<br>\n";
        if (strlen(trim($value))>0)
        {
            $fields_with_content++;
            $value = trim(str_replace("\r", "", $value));       // remove Windows specific CR characters
            $sql .= $sep.'`'.preg_replace('%[^a-zA-Z0-9_ ]%', '', $key)."`='".mysql_real_escape_string($value)."'";
            $sep = ', ';
        } else
        {
            $empty_fields++;
        }
    }

    echo "<br><hr><br>\nFields with contents: $fields_with_content<br>\n";
    echo "Empty fields: $empty_fields<br>\n";
    echo htmlspecialchars($sql)."<br>\n";

    exit;
}

?>
<!DOCTYPE HTML>
<html>
<head>
 <title>scrchpst input shizzles</title>
 <meta http-equiv="content-type" content="text/html; charset=UTF-8">
 <style type="text/css">
body        { max-width: 450px; font-family: constantia, cambria, times; font-size: 12px; background: #E0E0E0; color: #000000; margin: 50px; }
h1          { font-family: calibri, tahoma, verdana; color: #003080; font-size: 25px; margin: 17px 0px 9px 0px; border: #B0B0B0 solid; border-width: 0px 0px 1px 0px; }
h2          { font-family: calibri, tahoma, verdana; color: #003080; font-size: 19px; margin: 15px 0px 5px 0px; }
h3          { font-family: calibri, tahoma, verdana; color: #003080; font-size: 15px; margin: 13px 0px 5px 0px; }
textarea    { width: 313px; height: 150px; }
 </style>
</head>
<body>

<form action="arrayinput.php" method="post">
<h1>Type in stuff</h1>
<input type="text" name="first_name" placeholder="First name">
<input type="text" name="last_name" placeholder="Last name"><br>
<textarea name="description"></textarea><br>
<input type="submit" value="OK">
</form>

</body>
</html>