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https://issues.apache.org/jira/browse/FLINK-40826?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated FLINK-40826:
-----------------------------------
Labels: pull-request-available (was: )
> Support casting constructed types to VARIANT
> ---------------------------------------------
>
> Key: FLINK-40826
> URL: https://issues.apache.org/jira/browse/FLINK-40826
> Project: Flink
> Issue Type: Sub-task
> Components: Table SQL / API
> Reporter: Ramin Gharib
> Assignee: Ramin Gharib
> Priority: Major
> Labels: pull-request-available
>
> Adds {{CAST}} from primitive types to VARIANT. This ticket adds ARRAY, MAP,
> ROW, and STRUCTURED sources.
> h3. Rule
> A constructed type casts to VARIANT only if every leaf type does. Each level
> maps to its VARIANT shape, and each leaf is cast by the primitive rule. A
> leaf without a VARIANT kind rejects the whole cast at validation time.
> ||Source type||Stored VARIANT shape||
> |ARRAY<T>|array, each element cast from T|
> |MAP<K, V>|object, K must be a character string, each value cast from V|
> |ROW, STRUCTURED|object keyed by field name|
> {code:sql}
> CAST(ARRAY[1, 2, 3] AS VARIANT) -- [1,2,3]
> CAST(ARRAY[1, NULL] AS VARIANT) -- [1,null], a NULL element
> becomes a variant null
> CAST(MAP['a', 1, 'b', 2] AS VARIANT) -- \{"a":1,"b":2}
> CAST(r AS VARIANT) -- \{"id":7,"name":"ada"}
> for r ROW<id INT, name STRING>
> CAST(r AS VARIANT) -- \{"id":1,"tags":[1,2]}
> for r ROW<id INT, tags VARIANT>
> CAST(MAP[1, 'a'] AS VARIANT) -- fails at validation, keys
> are not stringified
> CAST(ARRAY[INTERVAL '1' DAY] AS VARIANT) -- fails at validation, the
> leaf has no VARIANT kind
> CAST(MULTISET[1, 1] AS VARIANT) -- fails at validation
> {code}
> * A NULL element, map value, or field becomes a variant null, so the array
> length and the object shape are kept. A NULL top-level value stays SQL NULL.
> * A nested VARIANT is embedded as is.
> * Field order is not kept, since a variant object is ordered by key.
> * An empty array, map, or row becomes an empty array or object.
> This can be delivered in three PRs, ARRAY, then MAP, then ROW and STRUCTURED,
> like the opposite direction in FLINK-37926.
> h3. Open question
> Which keys should an unnamed row get? The SQL row constructor {{ROW(7,
> 'ada')}} carries planner-generated field names that are not user-facing.
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