alamb commented on a change in pull request #1719:
URL: https://github.com/apache/arrow-datafusion/pull/1719#discussion_r796067705
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File path: datafusion/src/optimizer/simplify_expressions.rs
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@@ -662,6 +664,48 @@ impl<'a> ExprRewriter for Simplifier<'a> {
_ => unreachable!(),
},
+ //
+ // Rules for Case
+ //
+
+ // CASE
+ // WHEN X THEN A
+ // WHEN Y THEN B
+ // ...
+ // ELSE Q
+ // END
+ //
+ // ---> (X AND A) OR (Y AND B AND NOT X) OR ... (NOT (X OR Y) AND
Q)
+ Case {
+ expr: None,
+ when_then_expr,
+ else_expr,
+ } if is_boolean_expr => {
+ // The disjunction of all the when predicates encountered so
far
Review comment:
Given the complexity of expression this could potentially produce
`O(n!)` maybe in terms of the number of `when` exprs (I think?), what do you
think about adding a heuristic that only does this rewrite when there are a
'small' number of cases -- perhaps 2 or 3?
This would prevent some sort of pathological explosion and would handle the
usecase of simple mapping `CASE` statements
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