private static function esc_sql_value( $values ) {
		$quote = function ( $v ) {
			// Don't quote integer values to avoid MySQL's implicit type conversion.
			if ( preg_match( '/^[+-]?[0-9]{1,20}$/', $v ) ) { // MySQL BIGINT UNSIGNED max 18446744073709551615 (20 digits).
				return esc_sql( $v );
			}

			// Put any string values between single quotes.
			return "'" . esc_sql( $v ) . "'";
		};

		if ( is_array( $values ) ) {
			return array_map( $quote, $values );
		}

		return $quote( $values );
	}