public function by_related_to_max( $by_meta_keys, $max, $keys = null, $values = null ) {
		$max = $this->prepare_value( $max, '%d' );

		/** @var wpdb $wpdb */
		global $wpdb;

		$join      = '';
		$and_where = '';
		if ( ! empty( $keys ) || ! empty( $values ) ) {
			$join = "\nJOIN {$wpdb->postmeta} pm2 ON pm1.post_id = pm2.post_id\n";
		}
		if ( ! empty( $keys ) ) {
			$keys      = $this->prepare_interval( $keys );
			$and_where .= "\nAND pm2.meta_key IN {$keys}\n";
		}
		if ( ! empty( $values ) ) {
			$values    = $this->prepare_interval( $values );
			$and_where .= "\nAND pm2.meta_value IN {$values}\n";
		}

		$by_meta_keys = $this->prepare_interval( $by_meta_keys );

		$this->where_clause( "{$wpdb->posts}.ID IN (
			SELECT pm1.meta_value
			FROM {$wpdb->postmeta} pm1 {$join}
			WHERE pm1.meta_key IN {$by_meta_keys} {$and_where}
			GROUP BY( pm1.meta_value )
			HAVING COUNT(DISTINCT pm1.post_id) <= {$max}
		)" );

		return $this;
	}