Get month and years from list of custom post in wp

functions.php

<?php
$yearsStart = $wpdb->get_col("SELECT YEAR(FROM_UNIXTIME((meta_value / 1000))) FROM wp_postmeta WHERE meta_key LIKE 'start_date' ORDER BY meta_value ASC");
$yearsEnd = $wpdb->get_col("SELECT YEAR(FROM_UNIXTIME((meta_value / 1000))) FROM wp_postmeta WHERE meta_key LIKE 'end_date' ORDER BY meta_value ASC");
$tempyears = array_unique(array_merge($yearsStart, $yearsEnd));

$currentYear = date('Y');
$currentMonth = date('m');

foreach (array_unique($yearsStart) as $year) {
  if($year >= $currentYear) {
    $tempMonths = $wpdb->get_col("SELECT DISTINCT MONTH(FROM_UNIXTIME((meta_value / 1000))) FROM wp_postmeta WHERE meta_key LIKE 'start_date' AND YEAR(FROM_UNIXTIME((meta_value / 1000))) = $year ORDER BY meta_value ASC");
    foreach ($tempMonths as $month) {
      if($year > $currentYear OR $month >= $currentMonth) {
        $months[] = $month;
      }
    }
  }
}
?>