Allow execution of zero parameter functions

[jimexist]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

We shall allow the execution of zero parameter functions.

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One solution is to conventionally pass a null array with the correct expected batch size to ScalarFunctionImplementation so that functions with zero param can take that as input.

where the first param usize is the batch size

Describe alternatives you've considered
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Additional context
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[jorgecarleitao]

Some alternatives:

• create a node for these type of operations.

• have the physical planner pass a NullArray to functions of zero arguments; NullArray has a length (only has a length).

[jimexist]

@jorgecarleitao thanks for the advice. did you mean these two bullets combined as a solution?

[jorgecarleitao]

They are independent solutions:

In the former, we have a new PhysicalExpr, that executes evaluates in a different way (by passing the length to the function)

In the latter, the planner would query the number of arguments of the expression, and if it is zero, would pass a NullArray to it (I do not have the exact solution atm).

In my opinion this issue should be written in a generic form, so that it focus on the problem and not on the solution. E.g. instead of "Allow ScalarFunctionImplementation to...", use "Allow execution of zero-argument functions".

It is not obvious to me that changing the signature of ScalarFunctionImplementation is the right approach here.

[jimexist]

It is not obvious to me that changing the signature of ScalarFunctionImplementation is the right approach here.
Agree on this.

Let me rephrase