[CALCITE-1790] Simplify CASE P1 THEN <boolean> P@ THEN <booleans> ... ELSE TRUE/FALSE

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: core
• Assignee: Remus Rusanu
• Reporter: Remus Rusanu
• Created: 12/May/17 08:26
• Updated: 23/May/17 21:43

Description

In HIVE-14431 jcamachorodriguez proposed a simplification for CASE when all branches are not nullable 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:

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

to be transformed into:

(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(p1) AND not(p2) ... AND not(pn))]

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

Issue Links

• is related to: CALCITE-1290 When converting to CNF, fail if the expression size exceeds a threshold
• relates to: CALCITE-1794 Expressions with numeric comparisons are not simplified when CAST is present