petern48 commented on code in PR #17602:
URL: https://github.com/apache/datafusion/pull/17602#discussion_r2353355705
##########
datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs:
##########
@@ -1400,13 +1400,40 @@ impl<S: SimplifyInfo> TreeNodeRewriter for
Simplifier<'_, S> {
//
// CASE WHEN true THEN A ... END --> A
+ // CASE WHEN X THEN A WHEN TRUE THEN B ... END --> CASE WHEN X
THEN A ELSE B END
Expr::Case(Case {
expr: None,
mut when_then_expr,
- else_expr: _,
- }) if !when_then_expr.is_empty() &&
is_true(when_then_expr[0].0.as_ref()) => {
- let (_, then_) = when_then_expr.swap_remove(0);
- Transformed::yes(*then_)
+ else_expr,
+ // if let guard is not stabilized so we can't use it yet:
https://github.com/rust-lang/rust/issues/51114
+ // Once it's supported we can avoid searching through
when_then_expr twice in the below .any() and .position() calls
+ // }) if let Some(i) = when_then_expr.iter().position(|(when,
_)| is_true(when.as_ref())) => {
+ }) if when_then_expr
+ .iter()
+ .any(|(when, _)| is_true(when.as_ref())) =>
+ {
+ if let Some(i) = when_then_expr
+ .iter()
+ .position(|(when, _)| is_true(when.as_ref()))
+ {
Review Comment:
Removing the condition guard results in making the case rule below this one
inaccessible, so we can't just remove the `.any()` condition here. An
alternative approach would be to move all of this logic into the same block as
the rule below this, but the code wouldn't be so clean. I feel like iterating
over the `when_then_expr` vector twice for now isn't too bad since these
shouldn't really get too long, but I'm happy to hear other thoughts.
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