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-576531353
 
 
   > Vladimir, did you check what happens if a table function returns null and 
it is an argument to a consuming table function?
   
   `null` argument is just a null argument. Arguments are never converted to an 
empty relation.
   
   Note: Oracle schema does not make the distinction between `regular 
functions` and `table functions`. A function can be used as a table function if 
it returns a collection.
   However, the very same function can be used in `SELECT` or in `PL/SQL`, and 
`null` values are allowed for collections.
   
   So I think it should be fine to return null from Calcite's table function, 
however, the executor should treat `table(null)` as an empty relation of the 
appropriate type.

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