Hey It works very well....!!!! Thanks Peter Mortensen and Connor Burton
<?php
header("Content-type: application/csv");
header("Content-Disposition: attachment; filename=file.csv");
header("Pragma: no-cache");
header("Expires: 0");
ini_set('display_errors',1);
$private=1;
error_reporting(E_ALL ^ E_NOTICE);
mysql_connect("localhost", "user", "pass") or die(mysql_error());
mysql_select_db("db") or die(mysql_error());
$start = $_GET["start"];
$end = $_GET["end"];
$query = "SELECT * FROM customers WHERE created>='{$start} 00:00:00' AND created<='{$end} 23:59:59' ORDER BY id";
$select_c = mysql_query($query) or die(mysql_error());
while ($row = mysql_fetch_array($select_c, MYSQL_ASSOC))
{
$result.="{$row['email']},";
$result.="\n";
echo $result;
}
?>