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https://issues.apache.org/jira/browse/FLINK-40825?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated FLINK-40825:
-----------------------------------
Labels: pull-request-available (was: )
> Support casting primitive types to VARIANT
> ------------------------------------------
>
> Key: FLINK-40825
> URL: https://issues.apache.org/jira/browse/FLINK-40825
> Project: Flink
> Issue Type: Sub-task
> Components: Table SQL / API
> Reporter: Ramin Gharib
> Assignee: Ramin Gharib
> Priority: Major
> Labels: pull-request-available
>
> FLIP-521 lists the types that can be cast to and from VARIANT. FLINK-37925
> and FLINK-37926 implemented the direction VARIANT to SQL type. The direction
> SQL type to VARIANT is still missing: \{{SqlCastFunction}} rejects every cast
> to VARIANT (see the TODO in \{{canCastFrom}}).
> This ticket adds \{{CAST}} and \{{TRY_CAST}} from primitive types to VARIANT.
> Constructed types (ARRAY, MAP, ROW, STRUCTURED) follow in separate sub-tasks.
> h3. Rule
> A type can be cast to VARIANT only if a VARIANT kind holds its value without
> loss. Any other type is rejected at validation time, never at runtime. The
> cast is explicit only.
> ||Source type||Stored VARIANT kind||
> |BOOLEAN|BOOLEAN|
> |TINYINT, SMALLINT, INTEGER, BIGINT|TINYINT, SMALLINT, INT, BIGINT|
> |FLOAT, DOUBLE|FLOAT, DOUBLE|
> |DECIMAL(p, s)|DECIMAL|
> |CHAR, VARCHAR|STRING|
> |BINARY, VARBINARY|BYTES|
> |DATE, TIME, UUID|DATE, TIME, UUID|
> |TIMESTAMP(p), TIMESTAMP_LTZ(p)|TIMESTAMP, TIMESTAMP_LTZ, or the nanosecond
> kinds when the value has digits below a microsecond|
> Rejected: INTERVAL, TIMESTAMP WITH TIME ZONE, RAW, BITMAP, SYMBOL,
> DESCRIPTOR, MULTISET, and the constructed types for now.
> h3. Semantics
> {code:sql}
> CAST(CAST(1 AS BIGINT) AS VARIANT) -- 1, stored as BIGINT
> CAST(42 AS VARIANT) -- 42, stored as INT
> CAST('\{"a": 1}' AS VARIANT) -- the string '\{"a": 1}', not
> an object
> CAST(CAST(NULL AS INT) AS VARIANT) -- SQL NULL, not a variant null
> CAST(CAST('NaN' AS DOUBLE) AS VARIANT) -- NaN, stored as DOUBLE
> CAST(INTERVAL '2' DAY AS VARIANT) -- fails at validation
> CAST(ARRAY[1, 2] AS VARIANT) -- fails at validation,
> follow-up
> {code}
> * An integer keeps the width of its SQL type. \{{PARSE_JSON('1')}} picks the
> smallest kind because JSON text has no width, but a cast keeps the declared
> type.
> * A character string is wrapped as a STRING and never parsed. \{{PARSE_JSON}}
> remains the way to parse JSON text.
> * NaN and infinity are valid VARIANT values, since the binary format stores
> IEEE numbers. \{{PARSE_JSON}} rejects them only because JSON has no literal
> for them.
> * Every supported type round-trips: \{{CAST(CAST(x AS VARIANT) AS T) = x}}.
> * The cast never fails at runtime, so \{{TRY_CAST}} behaves like \{{CAST}}.
> h3. Prerequisite change
> Casting a VARIANT to FLOAT or DOUBLE rejected every non-finite result as an
> overflow. A VARIANT holding NaN, for example from the Avro converter, could
> therefore not be read back. The read now rejects only a finite value that
> does not fit, such as 1e40 to FLOAT, and keeps a stored NaN or infinity.
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