alamb commented on code in PR #17743:
URL: https://github.com/apache/datafusion/pull/17743#discussion_r2379533628
##########
datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs:
##########
@@ -1471,6 +1508,56 @@ impl<S: SimplifyInfo> TreeNodeRewriter for
Simplifier<'_, S> {
// Do a first pass at simplification
out_expr.rewrite(self)?
}
+ // CASE
+ // WHEN X THEN true
+ // WHEN Y THEN true
+ // WHEN Z THEN false
+ // ...
+ // ELSE true
+ // END
+ //
+ // --->
+ //
+ // NOT(CASE
+ // WHEN X THEN false
+ // WHEN Y THEN false
+ // WHEN Z THEN true
+ // ...
+ // ELSE false
+ // END)
+ //
+ // Note: the rationale for this rewrite is that the case can then
be further
Review Comment:
That is a great example, maybe we can add it to the comments (as a follow on
PR)
##########
datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs:
##########
@@ -1447,7 +1480,11 @@ impl<S: SimplifyInfo> TreeNodeRewriter for
Simplifier<'_, S> {
when_then_expr,
else_expr,
}) if !when_then_expr.is_empty()
- && when_then_expr.len() < 3 // The rewrite is O(n²) so limit
to small number
+ // The rewrite is O(n²) in general so limit to small number of
when-thens that can be true
+ && (when_then_expr.len() < 3 // small number of input whens
+ // or all thens are literal bools and a small number of
them are true
Review Comment:
Makes sense -- let's keep the check then
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