[GitHub] [calcite] vlsi edited a comment on issue #1593: [CALCITE-3513] Unify TableFunction implementor's NullPolicy and its behavior

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vlsi edited a comment on issue #1593: [CALCITE-3513] Unify TableFunction implementor's NullPolicy and its behavior
URL: https://github.com/apache/calcite/pull/1593#issuecomment-576206023
 
 
   Ok, so your main question is "what should Calcite do when a table function returns NPE"?
   
   Oracle makes it indistinguishable from an empty collection.
   
   For instance:
   
   ```sql
   select * from dual, table(cast(null as sys.odcinumberlist)) t;
   
   DUMMY | COLUMN_VALUE
   0 rows
   
   select * from dual, table(sys.odcinumberlist()) t;
   
   DUMMY | COLUMN_VALUE
   0 rows
   
   select * from dual, table(cast(null as sys.odcinumberlist))(+) t;
   DUMMY | COLUMN_VALUE
       Y | [NULL]
   1 row
   
   select * from dual, table(sys.odcinumberlist())(+) t;
   DUMMY | COLUMN_VALUE
       Y | [NULL]
   1 row
   ```
   
   > Therefore, NullPolicy.ANY/STRICT/ARG0 seems to be meaningless
   
   It is probably more to optimization and/or prevent invocation of the function on invalid inputs.
   For instance, if NullPolicy is set to `ANY`, then enumerable executor won't invoke the function in case there are null arguments.
   
   On the other hand, treating `null` table function result as an empty table is a different issue.

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