alamb commented on code in PR #17973:
URL: https://github.com/apache/datafusion/pull/17973#discussion_r2417644396
##########
datafusion/physical-expr/src/expressions/case.rs:
##########
@@ -431,6 +428,15 @@ impl CaseExpr {
_ => Cow::Owned(prep_null_mask_filter(when_value)),
};
+ let true_count = when_value.true_count();
+ if true_count == batch.num_rows() {
+ // Avoid evaluate_selection when all rows are true
+ return self.when_then_expr[0].1.evaluate(batch);
+ } else if true_count == 0 {
+ // Avoid evaluate_selection when all rows are false/null
+ return self.else_expr.as_ref().unwrap().evaluate(batch);
+ }
+
Review Comment:
My reading of this code is that it will still evaluate the `then` expression
as long as there is at least one true value in `when` -- if
`evaluate_selection` is a problem, shouldn't we fix `evaluate_selection`?
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