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https://issues.apache.org/jira/browse/SPARK-57618?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated SPARK-57618:
-----------------------------------
Labels: pull-request-available (was: )
> Support casting between TIME(p) and TIMESTAMP_NTZ(q)
> ----------------------------------------------------
>
> Key: SPARK-57618
> URL: https://issues.apache.org/jira/browse/SPARK-57618
> 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
>
> h2. Summary
> Add bidirectional ANSI casts between the {{TIME(p)}} data type (p in [0, 9])
> and
> {{TIMESTAMP_NTZ(q)}} (q in [6, 9]), where q=6 is the microsecond
> {{TimestampNTZType}}
> and q in [7, 9] is the nanosecond {{TimestampNTZNanosType}}.
> h2. Motivation
> Spark already supports {{TIME}} casts to/from {{STRING}}, integral, and
> {{DECIMAL}}
> types, but there is no way to convert between {{TIME}} and {{TIMESTAMP_NTZ}}.
> These
> conversions are required by the SQL standard and are a common user need (e.g.
> attaching
> a time-of-day to a timestamp, or extracting the time-of-day from a timestamp).
> h2. Semantics (SQL standard)
> * {{CAST(TIMESTAMP_NTZ(q) AS TIME(p))}} (standard rule 15.d): take the
> hour/minute/second
> and fractional fields of the source, truncated to precision {{p}}.
> Deterministic and
> time-zone independent.
> * {{CAST(TIME(p) AS TIMESTAMP_NTZ(q))}} (standard rule 17.c): the date fields
> come from
> {{CURRENT_DATE}} and the time fields come from the value. As {{CURRENT_DATE}}
> is stable
> within a query, the cast is stabilized via the existing
> {{ComputeCurrentTime}} rule so
> all references in a query observe the same date (matching {{current_date()}}).
> Fractional precision handling is pure truncation (no rounding). Both
> directions always
> succeed, so there is no new nullability or error condition.
> h2. Examples
> {code:sql}
> -- extract time-of-day
> SELECT CAST(TIMESTAMP_NTZ'2020-05-17 12:34:56.789012' AS TIME(6));
> -- 12:34:56.789012
> -- attach the current date
> SELECT CAST(TIME'12:34:56.789012345' AS TIMESTAMP_NTZ(9));
> -- <current_date> 12:34:56.789012345
> {code}
> h2. Scope
> * Allow the four cast pairs in both ANSI and non-ANSI modes (and TRY): TIME
> <-> the
> NTZ family only; TIMESTAMP_LTZ is intentionally not a valid counterpart.
> * Interpreted and codegen paths.
> * {{TIME -> TIMESTAMP_NTZ}} is stabilized within a query via
> {{ComputeCurrentTime}}.
> h2. Out of scope
> * Structured Streaming batch-timestamp parity for {{TIME -> TIMESTAMP_NTZ}}:
> the cast
> uses the optimizer-instant current date rather than the micro-batch timestamp.
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