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https://issues.apache.org/jira/browse/SPARK-57660?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated SPARK-57660:
-----------------------------------
Labels: pull-request-available (was: )
> Support casting between TIME(p) and TIMESTAMP_LTZ(q)
> ----------------------------------------------------
>
> Key: SPARK-57660
> URL: https://issues.apache.org/jira/browse/SPARK-57660
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 4.3.0
> Reporter: Max Gekk
> Assignee: Max Gekk
> Priority: Major
> Labels: pull-request-available
>
> Add bidirectional casts between the TIME(p) data type (p in [0, 9]) and
> TIMESTAMP_LTZ(q)
> (q in [6, 9], where q=6 is the microsecond TimestampType and q in [7, 9] is
> the
> nanosecond TimestampLTZNanosType).
> This is the TIMESTAMP_LTZ counterpart of SPARK-57618 (TIME <->
> TIMESTAMP_NTZ), and a
> sub-task of SPARK-56822 (timestamps with nanosecond precision).
> Semantics follow the SQL standard (section 6.13 <cast specification>):
> * CAST(TIMESTAMP_LTZ(q) AS TIME(p)) (rule 15.d): the LTZ value is an absolute
> instant, so
> its time-of-day is the local wall-clock time observed in the session time
> zone, truncated
> to precision p. Unlike TIMESTAMP_NTZ -> TIME, this direction depends on the
> session
> time zone.
> * CAST(TIME(p) AS TIMESTAMP_LTZ(q)) (rule 17.c): the date fields come from
> CURRENT_DATE and
> the time fields from the value; the resulting local date-time is
> interpreted in the
> session time zone to produce the instant. Since CURRENT_DATE is stable
> within a query, the
> cast is stabilized via the existing ComputeCurrentTime optimizer rule, so
> it shares the
> same date literal as current_date().
> Both directions of TIME <-> TIMESTAMP_LTZ therefore depend on the session
> time zone (whereas
> for TIMESTAMP_NTZ only TIME -> TIMESTAMP_NTZ does).
> Fractional precision handling is pure truncation (floor toward the precision
> step; no
> rounding). Both directions always succeed, so no new nullability or error
> condition is
> introduced. TIME and TIMESTAMP_LTZ have no common type, so the conversion is
> supported only
> as an explicit CAST; implicit coercion (UNION / coalesce / CASE WHEN) is
> still rejected.
> Examples:
> -- extract the time-of-day in the session time zone
> SELECT CAST(TIMESTAMP'2020-05-17 12:34:56.789012' AS TIME(6));
> -- 12:34:56.789012
> -- attach the current date, interpreted in the session time zone
> SELECT CAST(TIME'12:34:56.789012345' AS TIMESTAMP_LTZ(9));
> -- <current_date> 12:34:56.789012345
> Out of scope: Structured Streaming batch-timestamp parity for TIME ->
> TIMESTAMP_LTZ (the
> cast uses the optimizer-instant current date rather than the micro-batch
> timestamp).
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