Max Gekk created SPARK-57553:
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Summary: Support cast between TIME and TIMESTAMP_LTZ
Key: SPARK-57553
URL: https://issues.apache.org/jira/browse/SPARK-57553
Project: Spark
Issue Type: Sub-task
Components: SQL
Affects Versions: 4.3.0
Reporter: Max Gekk
h2. What
Support {{CAST}} in both directions between {{TIME}} and {{TIMESTAMP}} /
{{TIMESTAMP_LTZ}}
(the microsecond {{TimestampType}}).
h2. Why
ANSI SQL requires TIME <-> TIMESTAMP to be a valid cast. SPARK-52617 covers the
WITHOUT TIME ZONE variant; this ticket covers the WITH LOCAL TIME ZONE variant.
Unlike NTZ,
the LTZ direction is time-zone aware and uses the session time zone.
h2. Semantics (ANSI / session time zone)
* {{CAST(time AS TIMESTAMP_LTZ)}}: combine the time-of-day with
{{CURRENT_DATE}} in the
session time zone, then store as an absolute instant (epoch micros, UTC).
* {{CAST(ts_ltz AS TIME(q))}}: convert the instant to the session time zone,
take the
time-of-day, truncate fractional seconds to q.
h2. Scope
* {{canCast}}/{{canAnsiCast}} + runtime + codegen in {{Cast.scala}}, threading
the session
{{zoneId}} (as other TIMESTAMP_LTZ casts do).
* {{TIMESTAMP_LTZ}} has microsecond precision; casting from {{TIME(7..9)}}
truncates the
sub-microsecond digits (mark nullable only if applicable).
h2. Acceptance criteria
* Both directions correct across DST/zone boundaries; covered with explicit
session
time-zone tests.
* ANSI and non-ANSI modes; tests in {{CastSuiteBase}} and SQL golden files.
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