Materialization of nested queries

[Scott Fines <bf...@apple.com.INVALID>]

Hi all,

I’m hoping this question is super easy, but I’m running into a bit of a roadblock while researching Calcite, and thought maybe someone on here might be interested.

So imagine that you have a fairly simple nested data structure, like

TableName struct {
	a int,
	b struct {
		c float
	}
}

And you are wanting to issue the query `select a, b.c from TableName where c = 3.14`. Getting the basic table scan to plan properly is a pretty straightforward task. 

Now suppose that you want to define a materialization of the query `select a,b.c from TableName`. When I attempt this, the materialization is never used—I tracked it down and it’s because the SubstitutionVisitor does not appear to consider it a “true” substitution (mundane details below). 

So my question is this: Is this type of materialization possible? If so, how would I go about it? (In broad terms, at least).

Thanks for your help!

Scott Fines

Code details:

The SubstitutionVisitor runs into a situation where it finds that the MVT is an equivalent expression, but does not believe it to be a “true” substitution. Specifically, `targetDescendent != this.target`, so the substitution is discarded. I’m not sure of the reasoning for why the visitor requires object equality here, perhaps there is some more context I am missing?