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Simplify associative expressions with references #11733

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Simplify associative expressions with references #11733

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32 changes: 32 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 @@ -1348,6 +1348,17 @@ impl<'a, S: SimplifyInfo> TreeNodeRewriter for Simplifier<'a, S> {
//
Expr::Negative(inner) => Transformed::yes(distribute_negation(*inner)),

//
// Rules for Associativity
//
Expr::BinaryExpr(BinaryExpr {
left,
op: op @ (Operator::Plus | Operator::Multiply),
right,
}) if can_rearrange_literals(&left, op, &right) => {
Transformed::yes(rearrange_literals(*left, op, *right))
}

//
// Rules for Case
//
Expand Down Expand Up @@ -3189,6 +3200,27 @@ mod tests {
);
}

#[test]
fn simplify_associative() {
// i + 1 + 2 => i + 3
assert_eq!(simplify(col("c3") + lit(1) + lit(2)), (col("c3") + lit(3)));

// (i + 1) + 2 => i + 3
assert_eq!(
simplify((col("c3") + lit(1)) + lit(2)),
(col("c3") + lit(3))
);

// i * 2 * 3 => i * 6
assert_eq!(simplify(col("c3") * lit(2) * lit(3)), (col("c3") * lit(6)));

// (i * 2) * 3 => i * 6
assert_eq!(
simplify((col("c3") * lit(2)) * lit(3)),
(col("c3") * lit(6))
);
}

#[test]
fn simplify_expr_case_when_then_else() {
// CASE WHEN c2 != false THEN "ok" == "not_ok" ELSE c2 == true
Expand Down
42 changes: 42 additions & 0 deletions datafusion/optimizer/src/simplify_expressions/utils.rs
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@tinfoil-knight tinfoil-knight Jul 30, 2024 •
edited
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Doesn't handle all possible positions currently for an associative expression.

Eg:

(i + 1) + 2; i + 1 + 2 will resolve to i + 3

But something like these won't
(1 + i) + 2
2 + (i + 1)
2 + (1 + i)
1 + 2 + i

Original file line number Diff line number Diff line change
Expand Up @@ -341,3 +341,45 @@ pub fn distribute_negation(expr: Expr) -> Expr {
_ => Expr::Negative(Box::new(expr)),
}
}

pub fn can_rearrange_literals(left: &Expr, op: Operator, right: &Expr) -> bool {
if let Expr::BinaryExpr(BinaryExpr {
left: l_left,
op: l_op,
right: l_right,
}) = left
{
if l_op == &op
&& matches!(**l_left, Expr::Column(_))
&& matches!(**l_right, Expr::Literal(_))
&& matches!(right, Expr::Literal(_))
{
return true;
}
};
false
}

pub fn rearrange_literals(left: Expr, op: Operator, right: Expr) -> Expr {
if let Expr::BinaryExpr(BinaryExpr {
left: l_left,
op: l_op,
right: l_right,
}) = &left
{
if l_op == &op
&& matches!(**l_left, Expr::Column(_))
&& matches!(**l_right, Expr::Literal(_))
&& matches!(right, Expr::Literal(_))
{
let right_expr = Expr::BinaryExpr(BinaryExpr {
left: l_right.clone(),
op,
right: Box::new(right),
});
return Expr::BinaryExpr(BinaryExpr::new(l_left.clone(), op, Box::new(right_expr)));
}
};

Expr::BinaryExpr(BinaryExpr::new(Box::new(left), op, Box::new(right)))
}
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