[jira] [Created] (CALCITE-1790) Simplify CASE P1 THEN P@ THEN ... ELSE TRUE/FALSE

["Remus Rusanu (JIRA)" <ji...@apache.org>]

Remus Rusanu created CALCITE-1790:
-------------------------------------

             Summary: Simplify CASE P1 THEN <boolean> P@ THEN <booleans> ...  ELSE TRUE/FALSE
                 Key: CALCITE-1790
                 URL: https://issues.apache.org/jira/browse/CALCITE-1790
             Project: Calcite
          Issue Type: Improvement
          Components: core
            Reporter: Remus Rusanu
            Assignee: Remus Rusanu
            Priority: Minor


In HIVE-14431 [~jcamachorodriguez] proposed a simplification for CASE when all branches are boolean expression into an alternative AND/OR/NOT based expression. This allows for more aggressive reductions and split/push-down on the whole.  Meantime the simplifier code migrated to Calcite so I'm reviving this here.

The proposed simplification is:

{code}
CASE
WHEN p1 THEN ex1
WHEN p2 THEN ex2
...
WHEN pn THEN exn
ELSE TRUE/FALSE
END
{code}

to be transformed into:
{code}
(p1 AND ex1)
OR (not(p1) AND p2 AND x2)
...
OR (not(p1) AND not(p2) ... AND not(pn-1) AND Pn AND exn)
OR [not] (not(p1) AND not(p2) ... AND not(pn))
{code}

The last OR is negated depending on the ELSE branch being TRUE/FALSE.



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