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feat: Simplify CASE WHEN true THEN expr to expr #17450

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feat: Simplify CASE WHEN true THEN expr to expr #17450

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67 changes: 67 additions & 0 deletions datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1399,6 +1399,18 @@ impl<S: SimplifyInfo> TreeNodeRewriter for Simplifier<'_, S> {
// Rules for Case
//

// CASE WHEN true THEN A ... END --> A
Expr::Case(Case {
expr: None,
when_then_expr,
else_expr: _,
}) if !when_then_expr.is_empty()
&& matches!(when_then_expr[0].0.as_ref(),
Expr::Literal(ScalarValue::Boolean(Some(true)), _)) =>
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can we please use is_true to follow the pattern in the rest of this method?

datafusion/datafusion/optimizer/src/simplify_expressions/utils.rs

Lines 193 to 198 in 4b9a468

pub fn is_true(expr: &Expr) -> bool {
match expr {
Expr::Literal(ScalarValue::Boolean(Some(v)), _) => *v,
_ => false,
}
}

{
Transformed::yes((*when_then_expr[0].1).clone())
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I think it would be good to avoid this clone too,

How about something like this:

Suggested change
Transformed::yes((*when_then_expr[0].1).clone())
let (when, then_) = when_then_expr.swap_remove(0);
Transformed::yes(*when)

}

// CASE
// WHEN X THEN A
// WHEN Y THEN B
Expand Down Expand Up @@ -3552,6 +3564,61 @@ mod tests {
);
}

#[test]
fn simplify_expr_case_when_true() {
// CASE WHEN true THEN 1 ELSE x END --> 1
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can we please add some negative tests too -- like CASE WHEN a THEN 1 ELSE 2 END?

assert_eq!(
simplify(Expr::Case(Case::new(
None,
vec![(
Box::new(lit(true)),
Box::new(lit(1)),
)],
Some(Box::new(col("x"))),
))),
lit(1)
);

// CASE WHEN true THEN col("a") ELSE col("b") END --> col("a")
assert_eq!(
simplify(Expr::Case(Case::new(
None,
vec![(
Box::new(lit(true)),
Box::new(col("a")),
)],
Some(Box::new(col("b"))),
))),
col("a")
);

// CASE WHEN true THEN col("a") WHEN col("x") > 5 THEN col("b") ELSE col("c") END --> col("a")
assert_eq!(
simplify(Expr::Case(Case::new(
None,
vec![
(Box::new(lit(true)), Box::new(col("a"))),
(Box::new(col("x").gt(lit(5))), Box::new(col("b"))),
],
Some(Box::new(col("c"))),
))),
col("a")
);

// CASE WHEN true THEN col("a") END --> col("a") (no else clause)
assert_eq!(
simplify(Expr::Case(Case::new(
None,
vec![(
Box::new(lit(true)),
Box::new(col("a")),
)],
None,
))),
col("a")
);
}

fn distinct_from(left: impl Into<Expr>, right: impl Into<Expr>) -> Expr {
Expr::BinaryExpr(BinaryExpr {
left: Box::new(left.into()),
Expand Down
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