Wordpress export custom data to CSV

export-custom-data-to-csv.php

<?php
  if (isset($_GET['download-users'])) {
    global $wpdb;
    // Fetch data from a sepecific table(wp_users) from database 
    $query = $wpdb->get_results("SELECT * FROM `wp_users`"); 
    $filename = "wp_users_" . date('Y-m-d') . ".csv"; 
    $path = wp_upload_dir();   // or where ever you want the file to go
    $outstream = fopen( 'php://output', 'w' );
    $user_fields_csv = array('Row','ID','user_login','user_pass','user_email','user_registered');
    ob_end_clean();
    header( "Content-Disposition: attachment; filename={$filename}" );
    fputcsv( $outstream, $user_fields_csv );
    foreach ($query as $key => $value) {
        $lineData = array($key, $value->ID, $value->user_login, $value->user_pass, $value->user_email, $value->user_registered); 
        fputcsv($outstream, $lineData); 
    } 
    exit();
  }
?>
<a href="/?download-users">Download users</a>