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From Julian Hyde <>
Subject Re: Working with a RexCall tree in Filter
Date Fri, 06 Mar 2015 18:21:54 GMT
There are two classical approaches to expression evaluation - compilation and interpreting.
Calcite has both:

EnumerableFilter uses compilation. It converts its expression into Java code, using a RexToLixTranslator
(more precisely the EnumerableFilter is converted first to an EnumerableCalc, which is capable
of doing filters and projects; see how EnumerableCalc.implement calls RexToLixTranslator.convert).

BindableFilter uses interpretation. It creates a FilterNode, which calls Interpreter.compile
(a slight misnomer), which creates a Scalar. You can call scalar.execute(Context) and convert
the result to a Boolean.

(The current implementation of Interpreter.compile happens to work by invoking the code-generation
but there’s no reason why it should remain that way.)


On Mar 6, 2015, at 10:02 AM, Hartman, Trevor <> wrote:

> I'm working on pushing down filtering. In my own Filter rel impl, I see `condition` is
represented as a RexCall, with the appropriate operations and operands.
> e.g. where id = 1 AND (photoCount > 0 OR quantity > 0) builds up a RexCall tree
with AND as the root op.
> To implement filtering, I need a method like:
> def passesFilter(expr: RexCall, fields: Map[String, Any]): Boolean
> As I scan my table, I'd check passesFilter for each row, passing in a Map with keys id,
photoCount and quantity in this case.
> In reality, I'd probably use a translator (implements RexVisitorImpl) to turn the RexCall
into a data structure that's easier to work with in Scala. However, looking through Calcite
source, I see some things like RexExecutor, which led me to wonder:
> Is there anything in Calcite that can help me define `passesFilter` without me having
to manually walk an expression tree and evaluate the conditions? The built-in Filter implementation
must be doing this already, but I'm not sure how or if I can reuse that.
> Thanks,
> Trevor

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