Find out if your WordPress blog contains posts with more than one category

mdm_wp_multiple_categories.php

<?php
/**
 * mdm_wp_multiple_categories.php
 *
 * Find out if your WordPress blog contains posts with more than one category.
 *
 * Use as a standalone page or a function with WordPress.
 *
 * Function uses param to return string message or count of posts with multiple categories.
 */
if (!defined('ABSPATH'))
{
	require_once($_SERVER['DOCUMENT_ROOT'] . '/wp-load.php');
	header('Content-type: text/plain');
	echo mdm_wp_multiple_categories(), "\r\n";
	exit;
}
/**
 * Counts posts with multiple categories
 *
 * @param bool $text
 * @return string|int
 * if ($text == true) return string: informative message
 * else return integer: count of posts with multiple categories
 */
function mdm_wp_multiple_categories($text = true)
{
	global $wpdb;
	$result = $wpdb->get_results("select ID from wp_posts where post_type = 'post' and post_status = 'publish'", ARRAY_N);
	if (!is_array($result) || empty($result))
	{
		return 'No posts were found';
	}
	$multiple = 0;
	$total = count($result);
	foreach ($result as $k => $v)
	{
		$cats = get_the_category($v[0]);
		// $cats is an array or false if no categories were found.
		// user cannot save a post without a category, but nothing is certain.
		// check for array first. PHP expressions are evaluated left to right.
		if ( is_array( $cats ) && count( $cats ) > 1 )
		{
			$multiple++;
		}
	} // end foreach

	return $text ? "{$multiple} / {$total} posts have multiple categories" : $multiple;
} // end mdm_wp_multiple_categories
?>

Updated November 28, 2014

• Removed Exceptions.
• Display message if no posts were found.
• Ignore posts without categories.
• See: Do You Have WordPress Posts with Multiple Categories?