presto-main/src/main/java/io/prestosql/operator/scalar/DateTimeFunctions.java/DateTimeFunctions/diffTimeWithTimeZone
class DateTimeFunctions:    @Description("difference of the given times in the given unit")
    @ScalarFunction("date_diff")
    @LiteralParameters("x")
    @SqlType(StandardTypes.BIGINT)
    public static long diffTimeWithTimeZone(
            @SqlType("varchar(x)") Slice unit,
            @SqlType(StandardTypes.TIME_WITH_TIME_ZONE) long timeWithTimeZone1,
            @SqlType(StandardTypes.TIME_WITH_TIME_ZONE) long timeWithTimeZone2)
    {
        return getTimeField(unpackChronology(timeWithTimeZone1), unit).getDifferenceAsLong(unpackMillisUtc(timeWithTimeZone2), unpackMillisUtc(timeWithTimeZone1));
    }