Lattice on views not supported?

[maneesh varshney <mv...@gmail.com>]

Wanted to learn if this is by design.

Consider two tables: 'Fact' and 'Dim'. If we create two views FactView and
DimView (say, simple SELECT *), we cannot use these views in lattice
definition.

The Lattrice#populate (link below) only allows TableScan leaf nodes.
This method throws exception "Invalid node type LogicalProject in lattice
query"

https://github.com/apache/calcite/blob/67ece68208af8385c9e06b6b5cc812d6ad36293c/core/src/main/java/org/apache/calcite/materialize/Lattice.java#L181

I am still struggling to figure out why views (LogicalProject) should not
be allowed here. Any pointer will help.

Thanks!

Re: Lattice on views not supported?

[Julian Hyde <jh...@apache.org>]

It's a bug. Please file it.

We didn't prioritize lattices on views because the main purpose of
lattices is to optimize storage, i.e. recognize join-aggregate queries
on base tables and create aggregate tables with the same contents. At
runtime the system never sees queries on views, because the views will
have been expanded to their base tables.

I haven't thought about it much, but it may make sense to define
lattices on simple views (e.g. with a WHERE and/or inner JOIN) but
less sense to define lattices on more complex views (e.g. with MINUS,
or GROUP BY, or outer JOIN).

Julian

On Fri, Jan 15, 2021 at 10:22 AM maneesh varshney <mv...@gmail.com> wrote:
>
> Wanted to learn if this is by design.
>
> Consider two tables: 'Fact' and 'Dim'. If we create two views FactView and
> DimView (say, simple SELECT *), we cannot use these views in lattice
> definition.
>
> The Lattrice#populate (link below) only allows TableScan leaf nodes.
> This method throws exception "Invalid node type LogicalProject in lattice
> query"
>
> https://github.com/apache/calcite/blob/67ece68208af8385c9e06b6b5cc812d6ad36293c/core/src/main/java/org/apache/calcite/materialize/Lattice.java#L181
>
> I am still struggling to figure out why views (LogicalProject) should not
> be allowed here. Any pointer will help.
>
> Thanks!