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https://issues.apache.org/jira/browse/CALCITE-6896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18069667#comment-18069667
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hongyu guo commented on CALCITE-6896:
-------------------------------------
I don't think is a bug, I wrote a test in UdfTest.java, Timestamp can be
correctly converted to each other.
{code:java}
@Test void testTimestampRoundTripIsStable() {
final CalciteAssert.AssertThat with = withUdf();
with.query("values \"adhoc\".\"toTimestampFun\"(1741363199000)")
.returnsValue("2025-03-07 15:59:59");
with.query("values \"adhoc\".\"timestampFun\"(TIMESTAMP '2025-03-07
15:59:59')")
.returnsValue("1741363199000");
with.query("values
\"adhoc\".\"timestampFun\"(\"adhoc\".\"toTimestampFun\"(1741363199000))")
.returnsValue("1741363199000");
} {code}
> Improper Timezone Handling in SqlFunctions#internalToTimestamp
> ---------------------------------------------------------------
>
> Key: CALCITE-6896
> URL: https://issues.apache.org/jira/browse/CALCITE-6896
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.39.0
> Reporter: Wei.Zhou
> Priority: Major
>
> {*}Error Cause{*}: Improper Timezone Handling in method of
> SqlFunctions.internalToTimestamp(long v)
> # {{LocalDateTime.ofEpochSecond()}} generates a UTC-based timestamp but
> produces a *timezone-less* {{LocalDateTime}} object.
> # {{Timestamp.valueOf(dateTime)}} implicitly uses the *JVM's default
> timezone* to interpret the {{{}LocalDateTime{}}}, rather than preserving the
> UTC context. This creates a hidden timezone conversion.
> {*}Example{*}:
> If {{v = 1741363199000}} (UTC epoch: 2025-03-07 15:59:59) and the system
> timezone is UTC+8:
> * {{LocalDateTime}} correctly represents 2025-03-07 15:59:59 (UTC)
> * {{Timestamp.valueOf()}} treats it as 2025-03-07 15:59:59 {*}in UTC+8{*},
> resulting in an actual UTC time of 2025-03-07 7:59:59.000 (8-hour offset
> error).
> {*}Correct Approach{*}:
> {code:java}
> // Direct conversion without timezone ambiguity
> public static java.sql.Timestamp internalToTimestamp(long v) {
> return new java.sql.Timestamp(v); // Milliseconds directly map to SQL
> Timestamp
> }
> // Or using Instant
> public static java.sql.Timestamp internalToTimestamp(long v) {
> return Timestamp.from(Instant.ofEpochMilli(v));
> } {code}
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