EeshanBembi commented on code in PR #17602:
URL: https://github.com/apache/datafusion/pull/17602#discussion_r2353529356
##########
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()))
+ {
+ let (_, then_) = when_then_expr.swap_remove(i);
+ // CASE WHEN true THEN A ... END --> A
+ if i == 0 {
+ return Ok(Transformed::yes(*then_));
+ }
+ // CASE WHEN X THEN A WHEN TRUE THEN B ... END --> CASE
WHEN X THEN A ELSE B END
+ let truncated_when_then_expr =
when_then_expr[..i].to_vec();
Review Comment:
Performance / allocation nit (optional)
You currently build `truncated_when_then_expr` via a slice clone:
```rust
let truncated_when_then_expr = when_then_expr[..i].to_vec();
```
Since when_then_expr is already mut, you can avoid an allocation and extra
copies by truncating in place:
```
when_then_expr.truncate(i);
let truncated_when_then_expr = when_then_expr;
```
This eliminates the to_vec() allocation and is more efficient, especially
for larger CASE expressions.
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