Came across this nice little bit of code to write a CSV file on the fly using PHP and grabbing the data from a MySQL database. Thank you Stephen Morley for authoring a great little how to.
// output headers so that the file is downloaded rather than displayed
header('Content-Type: text/csv; charset=utf-8');
header('Content-Disposition: attachment; filename=data.csv');
// create a file pointer connected to the output stream
$output = fopen('php://output', 'w');
// output the column headings
fputcsv($output, array('Column 1', 'Column 2', 'Column 3'));
// fetch the data
mysql_connect('localhost', 'username', 'password');
mysql_select_db('database');
$rows = mysql_query('SELECT field1,field2,field3 FROM table');
// loop over the rows, outputting them
while ($row = mysql_fetch_assoc($rows)) fputcsv($output, $row);