[Bug] hour/minute/second expressions incorrectly apply timezone conversion to TimestampNTZ inputs

[andygrove]

Summary

The hour, minute, and second expressions (and potentially other timestamp extraction functions) incorrectly apply timezone conversion when the input is a TimestampNTZ (timestamp without timezone) value.

Root Cause

In native/spark-expr/src/datetime_funcs/extract_date_part.rs, the implementation uses array_with_timezone:

let array = array_with_timezone(
    array,
    self.timezone.clone(),
    Some(&DataType::Timestamp(
        Microsecond,
        Some(self.timezone.clone().into()),
    )),
)?;

For a TimestampNTZ input (Timestamp(Microsecond, None)), this calls timestamp_ntz_to_timestamp in utils.rs, which converts the local time value to UTC by applying the session timezone offset.

Expected Behavior

For TimestampNTZ inputs:

• Values are stored as local time without any timezone information
• hour(timestamp_ntz_value) should return the hour component directly from the local time value
• No timezone conversion should be applied

For Timestamp (with timezone) inputs:

• Values are stored in UTC
• hour(timestamp_value) should convert from UTC to the session timezone before extracting the hour
• This is the current behavior and is correct

Example

-- With session timezone = America/Los_Angeles (UTC-8)
-- TimestampNTZ value representing "2024-01-15 10:30:00" local time
-- 
-- Expected: hour() = 10 (extract directly from local time)
-- Actual (bug): hour() = 18 (incorrectly converts assuming value is in UTC)

Affected Functions

• hour (SparkHour)
• minute (SparkMinute)
• second (SparkSecond)

All three use the same extract_date_part! macro with array_with_timezone.

Impact

This bug can cause incorrect results when using hour/minute/second functions on TimestampNTZ columns in non-UTC timezones. Currently the Scala serde layer does not validate input types, so TimestampNTZ inputs are not blocked.

Suggested Fix

Either:

1. Add input type validation in the Scala serde layer (like CometUnixTimestamp) to mark TimestampNTZ as unsupported and fall back to Spark
2. Fix the Rust implementation to handle TimestampNTZ correctly by not applying timezone conversion

Option 1 is safer as a short-term fix.

Related

• Issue Implement Spark-compatible CAST to/from TimestampNTZType #378: Implement Spark-compatible CAST to/from TimestampNTZType
• Issue [EPIC] [DISCUSS] Comet timezone handling #2733: [EPIC] Comet timezone handling
• Issue [Bug] String to TimestampNTZ cast incorrectly produces timestamp with UTC timezone #3179: String to TimestampNTZ cast bug

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Note: This issue was generated with AI assistance.

[vigneshsiva11]

While implementing the Rust-side fix to bypass timezone conversion for TimestampNTZ, I noticed the alternative suggestion of blocking TimestampNTZ inputs at the Scala serde layer.

Question: Is the preferred long-term direction to fully support Spark-compatible TimestampNTZ semantics in the Rust implementation, or is TimestampNTZ expected to remain unsupported (and explicitly rejected) until the broader timezone handling work in Comet is completed?

I want to make sure the fix aligns with the intended roadmap and doesn’t conflict with upcoming timezone changes.

[andygrove]

@vigneshsiva11 We would eventually like to fully support TimestampNTZ. You may be interested in reviewing #3253

[vigneshsiva11]

Thanks for pointing me to #3253 I went through the PR.

It looks like the broader TimestampNTZType support there (casts, unix_timestamp, and temporal semantics without timezone conversion) aligns well with the intent behind my fix for hour/minute/second.

I’m happy to adjust or rebase my change on top of #3253 or help integrate the extract_date_part logic into that PR if you’d prefer to handle this as part of the larger TimestampNTZ support work. Please let me know what direction you think makes the most sense.