[
https://issues.apache.org/jira/browse/CALCITE-2450?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16572183#comment-16572183
]
Julian Hyde commented on CALCITE-2450:
--------------------------------------
I am not keen on re-ordering predicates. Sometimes lists need to be ordered for
safety (e.g. if we're going to generate code from "x is not null and x > 1" or
"x > 0 and y / x < 6"). Sometimes lists need to be ordered by selectivity (most
selective predicates first). This would break all that. Also, it would break
quite a few tests.
I am also not in favor of adding a field to every RexNode.
However I do think we should consider adding a "final boolean simplified" field
to a special sub-class of RexNode specifically for calls to AND. If
"simplified", we would know that operands are deduplicated, flattened (i.e.
none of them are ANDs). And -- this is up for debate -- they have been
simplified and constant-reduced.
AND is so common that this will help significantly.
> RexSimplify: reorder predicates to a canonical form as a part of RexSimplify
> ----------------------------------------------------------------------------
>
> Key: CALCITE-2450
> URL: https://issues.apache.org/jira/browse/CALCITE-2450
> Project: Calcite
> Issue Type: Sub-task
> Components: core
> Affects Versions: 1.17.0
> Reporter: Vladimir Sitnikov
> Assignee: Julian Hyde
> Priority: Major
>
> Certain optimizations are easier to perform when input expressions are in a
> canonical form.
> For instance: more duplicates can be found in AND/OR lists, case branches,
> etc.
> Note: this reordering is supposed to happen in RexSimplify only. In other
> words, RexBuilder would still produce "non-canonical" expressions.
> It is expected that {{RexSimplify}} might alter the expression, so if it
> converts {{5=x}} to {{x=5}} it should be just fine.
> The suggested rules are to be discussed, yet the following might be fine:
> 1) For AND, OR, IN: put "simpler" nodes first. The weight of a node could be
> either {{.toString().length()}} or a number of child nodes or something like
> that.
> The motivation is to simplify logic that handles "duplicate" entries. It
> won't have to consider "both alternatives" all over the place.
> 2) For comparison with literals put literal as the second argument
> 3) For binary comparison, put node with less weight to the left
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
