presto-main/src/main/java/io/prestosql/operator/scalar/DateTimeFunctions.java/DateTimeFunctions/diffTimestampWithTimeZone
class DateTimeFunctions:    @Description("difference of the given times in the given unit")
    @ScalarFunction("date_diff")
    @LiteralParameters("x")
    @SqlType(StandardTypes.BIGINT)
    public static long diffTimestampWithTimeZone(
            @SqlType("varchar(x)") Slice unit,
            @SqlType(StandardTypes.TIMESTAMP_WITH_TIME_ZONE) long timestampWithTimeZone1,
            @SqlType(StandardTypes.TIMESTAMP_WITH_TIME_ZONE) long timestampWithTimeZone2)
    {
        return getTimestampField(unpackChronology(timestampWithTimeZone1), unit).getDifferenceAsLong(unpackMillisUtc(timestampWithTimeZone2), unpackMillisUtc(timestampWithTimeZone1));
    }