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[jira] [Created] (CALCITE-2450) Reorder predicates to a canonical form as a part of RexSimplify

Vladimir Sitnikov created CALCITE-2450:

             Summary: 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

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

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