Github user adrian-wang commented on a diff in the pull request: https://github.com/apache/spark/pull/13784#discussion_r67795207 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala --- @@ -886,23 +886,45 @@ object DateTimeUtils { } /** + * Convert the timestamp `ts` from one timezone to another. + * + * TODO: Because of DST, the conversion between UTC and human time is not exactly one-to-one + * mapping, the conversion here may return wrong result, we should make the timestamp + * timezone-aware. + */ + def convertTz(ts: SQLTimestamp, fromZone: TimeZone, toZone: TimeZone): SQLTimestamp = { + // We always use local timezone to parse or format a timestamp + val localZone = threadLocalLocalTimeZone.get() + val utcTs = if (fromZone.getID == localZone.getID) { + ts + } else { + // get the human time using local time zone, that actually is in fromZone. + val localTs = ts + localZone.getOffset(ts / 1000L) * 1000L // in fromZone + localTs - getOffsetFromLocalMillis(localTs / 1000L, fromZone) * 1000L + } + if (toZone.getID == localZone.getID) { + utcTs + } else { + val localTs2 = utcTs + toZone.getOffset(utcTs / 1000L) * 1000L // in toZone + // treat it as local timezone, convert to UTC (we could get the expected human time back) + localTs2 - getOffsetFromLocalMillis(localTs2 / 1000L, localZone) * 1000L + } + } + + /** * Returns a timestamp of given timezone from utc timestamp, with the same string * representation in their timezone. */ def fromUTCTime(time: SQLTimestamp, timeZone: String): SQLTimestamp = { - val tz = TimeZone.getTimeZone(timeZone) - val offset = tz.getOffset(time / 1000L) - time + offset * 1000L + convertTz(time, TimeZoneGMT, TimeZone.getTimeZone(timeZone)) --- End diff -- For `fromUTCTime`, this would result in a little bit overhead.
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