Timo Walther created FLINK-36703:
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             Summary: FLIP-440: User-defined SQL operators / 
ProcessTableFunction (PTF)
                 Key: FLINK-36703
                 URL: https://issues.apache.org/jira/browse/FLINK-36703
             Project: Flink
          Issue Type: New Feature
          Components: Table SQL / API, Table SQL / Planner, Table SQL / Runtime
            Reporter: Timo Walther
            Assignee: Timo Walther


Introduce a new kind of user-defined function (UDF) that enables implementing 
user-defined SQL operators: [ProcessTableFunction 
(PTF)|https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=298781093]

The new UDF kind opens the Table & SQL API towards capabilities of the 
DataStream API while staying in the SQL ecosystem. And using all benefits of it.

PTFs look and feel familiar for both someone coming from the DataStream API 
world as well as the SQL world.

>From SQL:
 * Similar types and type inference as ScalarFunction, AggregateFunction, or 
TableFunction
 * Registration in catalog, usage of inline/temporary UDF, built-in system 
functions in the future
 * Usage in both SQL and Table API
 * Very important: Standard-compliant syntax using Polymorphic Table Functions 

>From DataStream API:
 * Familiar naming like ProcessFunction
 * Access to Map, List and Value state
 * Ability to both keyBy() and connect() streams. Long-term also broadcast side 
functionality.
 * Ability to deal with watermarks and dealing with time
 * Support of query evolution (terminology as defined in FLIP-190)



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