Dandandan commented on code in PR #22175:
URL: https://github.com/apache/datafusion/pull/22175#discussion_r3243003587
##########
datafusion/physical-expr/src/expressions/case.rs:
##########
@@ -268,14 +268,31 @@ struct ProjectedCaseBody {
/// [WHEN ...]
/// [ELSE result]
/// END
-#[derive(Debug, Hash, PartialEq, Eq)]
+#[derive(Debug)]
pub struct CaseExpr {
/// The case expression body
body: CaseBody,
/// Evaluation method to use
eval_method: EvalMethod,
}
+// eval_method is functionally derived from body, so excluding it from
+// Hash/Eq avoids redundantly hashing the expression tree twice. For
+// nested CASE chains this prevents exponential blowup (see #22173).
Review Comment:
```suggestion
// nested CASE chains this prevents exponential blowup (see
https://github.com/apache/datafusion/issues/22173).
```
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