[jira] [Updated] (FLINK-24311) Support expression reduction for JSON construction functions

["Flink Jira Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-24311?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Flink Jira Bot updated FLINK-24311:
-----------------------------------
    Labels: pull-request-available stale-major  (was: pull-request-available)

I am the [Flink Jira Bot|https://github.com/apache/flink-jira-bot/] and I help the community manage its development. I see this issues has been marked as Major but is unassigned and neither itself nor its Sub-Tasks have been updated for 60 days. I have gone ahead and added a "stale-major" to the issue". If this ticket is a Major, please either assign yourself or give an update. Afterwards, please remove the label or in 7 days the issue will be deprioritized.


> Support expression reduction for JSON construction functions
> ------------------------------------------------------------
>
>                 Key: FLINK-24311
>                 URL: https://issues.apache.org/jira/browse/FLINK-24311
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table SQL / API
>            Reporter: Ingo Bürk
>            Priority: Major
>              Labels: pull-request-available, stale-major
>
> For JSON construction functions such as JSON_OBJECT, we currently disable expression reduction. This is because these functions have special semantics where they behave differently depending on their call context. For example, JSON_OBJECT returns a JSON string. This means that a call like
> {code:java}
> JSON_OBJECT('A' VALUE JSON_OBJECT('B' VALUE 'C')){code}
> would result in
> {code:java}
> {"A": "{\"B\": \"C\"}"}{code}
> However, this is not user-friendly, and thus such nested calls are treated differently and instead result in the likely more intended outcome
> {code:java}
> {"A": {"B": "C"}}{code}
> To make this work, the function looks at its operands and checks whether each operand is another RexCall to such a JSON construction function. If it is, it inserts it as a raw node instead.
> This creates a problem during expression reduction. The RexCall will be replaced with a RexLiteral carrying the JSON string value. The function looking at the operands now cannot determine that this originated from such a RexCall anymore, and yields the unintended result once again. To prevent this, we currently disable expression reduction for these functions.
> We should aim to once again allow such expressions to be reduced while still preserving the intended behavior. See [this comment|https://github.com/apache/flink/pull/17186#issuecomment-920783089] for a rough idea of how this could be achieved.



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