WordPress - Query post/user meta

query-meta.php

<?php
/**
 * Query user meta table
 *
 * @param string|array $name_patt Meta key pattern match
 * @param string $query_suffix SQL query suffix
 * @param bool $post_meta Whether to query post meta table
 *
 * @return array|null Results of query
 */
function shramee_query_meta( $name_patt, $query_suffix = '', $post_meta = false ) {
	/** @var wpdb $wpdb */
	global $wpdb;

	$select = '`meta_key` as `key`, `meta_value` as `value`';

	if ( $post_meta ) {
		$table = $wpdb->postmeta;
		$select .= ', `post_id` as `id`';
	} else {
		$table = $wpdb->usermeta;
		$select .= ', `user_id` as `id`';
	}

	$name_patt = esc_sql( $name_patt );

	if ( is_array( $name_patt ) ) {
		$name_patt = implode( "' OR `meta_key` LIKE '", $name_patt );
	}

	return $wpdb->get_results(
		"SELECT {$select} FROM {$table} " .
		"WHERE ( `meta_key` LIKE '{$name_patt}' ) " .
		$query_suffix
	);
}