function exportCSVFile($file, $table, $fields = false, $where = false, $overwrite = false, $download = true, $headers = true) {
	//If Overwrite False, check if the file exists and make unique
	if(!$overwrite){
		if(file_exists($file)) { 
			$file = $file . "_" . time() . '.csv'; 
		}
	}
	
	// Check if download required
	if($download) {
        // send response headers to the browser
        header( 'Content-Type: text/csv' );
        header( 'Content-Disposition: attachment;filename='.$file);
        $fp = fopen('php://output', 'w');
    } else {
        $fp = fopen($file, 'w');
    }
    
	//The Query
	// Have fields been passed?
	if(!$fields) {
		$fields = "*";
	}
	// Has where clause been passed?
	if(!$where) {
		$where = "";
	}else{
		$where = "WHERE " . $where;
	}
	
	$query = "SELECT $fields FROM $table $where";
	
	$db = JFactory::getDBO();
	$db->setQuery($query);
    $result = $db->query($query);
   
    if($headers) {
        // output header row (if at least one row exists)
        $row = mysql_fetch_assoc($result);
        if($row) {
            fputcsv($fp, array_keys($row));
            // reset pointer back to beginning
            mysql_data_seek($result, 0);
        }
    }
   
    while($row = mysql_fetch_assoc($result)) {
	
			$line = "";
		    $comma = "";
		    foreach($row as $value) { //Escape quotes properly
		        $line .= $comma . '"' . str_replace('"', '""', $value) . '"';
		        $comma = ",";
		    }
		    $line .= "\n";
		    fputs($fp, $line);
    }
   	//Close the file
    fclose($fp);     
}

$export = exportCSVFile("your_filename.csv", "table_name", false, "WHERE your field = true");