Extend SHOW FUNCTIONS

[caithagoras]

== RELEASE NOTES ==

General Changes
* Add support to show whether functions have variable arity in ``SHOW FUNCTIONS``.
* Add support to show whether functions are built-in in ``SHOW FUNCTIONS``.

[caithagoras]

@rongrong Removed new session properties and configuration properties.
I think we should kept the column in a relative logical order (starting from more important attributes, to the less important metadata, and description at the end).

Column name suggestions are welcome if needed.

[rongrong]

I think we should kept the column in a relative logical order (starting from more important attributes, to the less important metadata, and description at the end).

Description is quite important (Personally I feel it's actually more important than type parameters and return types when I use SHOW FUNCTIONS). I agree it looks nicer to have all metadata together. My concern is mostly for backward compatibility. Nobody should use column orders though but you never know. For me the look doesn't worth it. But it's your call.

[rongrong]

This should be a function derived from RoutineCharacteristics.language. Actually is it better to expose language rather than implementation type?

[caithagoras]

Language is an attribute for SqlInvokedFunction only. If we expose this information as an agglomerated enum such as in (BUILTIN, SQL, PYTHON, JS...), I would avoid reuse the name language, maybe function type?

Also, as you mentioned, we may also want to ship SqlInvokedFunctions that are static and packaged within Presto, which type value do we give them? They are both BUILTIN and SQL, so use a new enum BUILTIN_SQL, or PREPACKAGED_SQL?

An alternative I would prefer is to introduce 2 columns instead.

• boolean built_in:
  • true: hard-coded functions, and pre-packaged SqlInvokedFunctions
  • false: user-defined functions.
• varchar language:
  • null: hard-coded functions
  • non-null values (SQL, Python, etc...): all SqlInvokedFunctions, including pre-packaged and user-defined.

I'm essentially defining "built_in" as anything that comes in with the presto installation, which I think does make sense.

[caithagoras]

@rongrong Separated into 2 columns: boolean builtin, varchar language