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Support equality with one in opt-in WindowTopN rule #26160

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Support equality with one in opt-in WindowTopN rule #26160

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40 changes: 38 additions & 2 deletions datafusion/physical-optimizer/src/window_topn.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,7 @@ use datafusion_physical_plan::windows::{BoundedWindowAggExec, WindowUDFExpr};
/// - `rn < K` → fetch = K - 1
/// - `K >= rn` (flipped) → fetch = K
/// - `K > rn` (flipped) → fetch = K - 1
/// - `rn = 1` or `1 = rn` → fetch = 1
///
/// # When the Rule Fires
///
Expand All @@ -121,7 +122,7 @@ use datafusion_physical_plan::windows::{BoundedWindowAggExec, WindowUDFExpr};
/// such as `PARTITION BY pk ORDER BY pk`; for `RANK` / `DENSE_RANK`
/// such orderings also make every row tie at rank 1 (degenerate).
/// - The filter predicate compares the window output column to an integer
/// literal using `<=`, `<`, `>=`, or `>`
/// literal using `<=`, `<`, `>=`, `>`, or equality with 1
///
/// [`PartitionedTopKExec`]: datafusion_physical_plan::sorts::partitioned_topk::PartitionedTopKExec
#[derive(Default, Clone, Debug)]
Expand Down Expand Up @@ -300,13 +301,16 @@ impl PhysicalOptimizerRule for WindowTopN {
/// | `Column(idx) < Literal(N)` | `(idx, N-1)` |
/// | `Literal(N) >= Column(idx)` | `(idx, N)` |
/// | `Literal(N) > Column(idx)` | `(idx, N-1)` |
/// | `Column(idx) = Literal(1)` | `(idx, 1)` |
/// | `Literal(1) = Column(idx)` | `(idx, 1)` |
///
/// # Examples
///
/// - `rn <= 5` → `Some((2, 5))` (assuming rn is column index 2)
/// - `rn < 3` → `Some((2, 2))`
/// - `10 >= rn` → `Some((2, 10))`
/// - `rn = 1` → `None` (equality not supported)
/// - `rn = 1` → `Some((2, 1))`
/// - `rn = 2` → `None` (removing the filter would include rank 1)
/// - `val <= 5` → `Some((1, 5))` (caller must verify it's a window column)
fn extract_window_limit(
predicate: &Arc<dyn datafusion_physical_expr::PhysicalExpr>,
Expand All @@ -325,6 +329,7 @@ fn extract_window_limit(
return match *op {
Operator::LtEq => Some((col.index(), n)),
Operator::Lt => Some((col.index(), n - 1)),
Operator::Eq if n == 1 => Some((col.index(), 1)),
_ => None,
};
}
Expand All @@ -338,6 +343,7 @@ fn extract_window_limit(
return match *op {
Operator::GtEq => Some((col.index(), n)),
Operator::Gt => Some((col.index(), n - 1)),
Operator::Eq if n == 1 => Some((col.index(), 1)),
_ => None,
};
}
Expand Down Expand Up @@ -411,3 +417,33 @@ fn find_window_below(plan: &Arc<dyn ExecutionPlan>) -> Option<PlanAndIntermediat
}
}
}

#[cfg(test)]
mod tests {
use super::*;
use datafusion_physical_expr::PhysicalExpr;

#[test]
fn equality_with_one_is_the_only_rewritable_equality() {
for (value, flipped, expected) in [
(Some(1), false, Some((2, 1))),
(Some(1), true, Some((2, 1))),
(Some(0), false, None),
(Some(2), false, None),
(Some(2), true, None),
(None, false, None),
] {
let column: Arc<dyn PhysicalExpr> = Arc::new(Column::new("rn", 2));
let literal: Arc<dyn PhysicalExpr> =
Arc::new(Literal::new(ScalarValue::UInt64(value)));
let (left, right) = if flipped {
(literal, column)
} else {
(column, literal)
};
let predicate: Arc<dyn PhysicalExpr> =
Arc::new(BinaryExpr::new(left, Operator::Eq, right));
assert_eq!(extract_window_limit(&predicate), expected);
}
}
}
55 changes: 43 additions & 12 deletions datafusion/sqllogictest/test_files/window_topn.slt
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Original file line number Diff line number Diff line change
Expand Up @@ -994,30 +994,61 @@ statement ok
DROP TABLE window_topn_rank_t;

###############################################################################
# RANK() — equality predicate (negative: rule supports only </<=/>=/>)
# Ranking functions — equality with one
###############################################################################
#
# `extract_window_limit` matches only `<, <=, >, >=`. Equality predicates
# `rk = N` are NOT optimized by this rule (regardless of N). DuckDB
# special-cases `rk = 1` as equivalent to `rk <= 1`; we don't. The two
# tests below pin current behavior so that an accidental rule extension
# (or regression) shows up.
# Ranking functions return positive integers, so `rank = 1` is equivalent to
# `rank <= 1`. Equality with larger values must retain the filter.

statement ok
CREATE TABLE window_topn_rank_eq_t (id INT, pk INT, val INT) AS VALUES
(1, 1, 10), (2, 1, 20), (3, 1, 30),
(1, 1, 10), (2, 1, 10), (3, 1, 20),
(4, 2, 5), (5, 2, 15), (6, 2, 25);

# Test R12: `rk = 1` — correct results, but plan should still contain
# FilterExec + SortExec (rule did NOT fire).
# Test R12: `rk = 1` keeps all tied winners.
query III rowsort
SELECT id, pk, val FROM (
SELECT *, RANK() OVER (PARTITION BY pk ORDER BY val) as rk FROM window_topn_rank_eq_t
) WHERE rk = 1;
----
1 1 10
2 1 10
4 2 5

query III rowsort
SELECT id, pk, val FROM (
SELECT *, RANK() OVER (PARTITION BY pk ORDER BY val) as rk FROM window_topn_rank_eq_t
) WHERE 1 = rk;
----
1 1 10
2 1 10
4 2 5

query III rowsort
SELECT id, pk, val FROM (
SELECT *, DENSE_RANK() OVER (PARTITION BY pk ORDER BY val) as rk FROM window_topn_rank_eq_t
) WHERE rk = 1;
----
1 1 10
2 1 10
4 2 5

query III rowsort
SELECT id, pk, val FROM (
SELECT *, ROW_NUMBER() OVER (PARTITION BY pk ORDER BY val, id) as rn FROM window_topn_rank_eq_t
) WHERE rn = 1;
----
1 1 10
4 2 5

# `rank = 2` is not equivalent to `rank <= 2`.
query III rowsort
SELECT id, pk, val FROM (
SELECT *, RANK() OVER (PARTITION BY pk ORDER BY val) as rk FROM window_topn_rank_eq_t
) WHERE rk = 2;
----
5 2 15

query TT
EXPLAIN SELECT * FROM (
SELECT *, RANK() OVER (PARTITION BY pk ORDER BY val) as rk FROM window_topn_rank_eq_t
Expand All @@ -1030,9 +1061,9 @@ logical_plan
04)------TableScan: window_topn_rank_eq_t projection=[id, pk, val]
physical_plan
01)ProjectionExec: expr=[id@0 as id, pk@1 as pk, val@2 as val, rank() PARTITION BY [window_topn_rank_eq_t.pk] ORDER BY [window_topn_rank_eq_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW@3 as rk]
02)--FilterExec: rank() PARTITION BY [window_topn_rank_eq_t.pk] ORDER BY [window_topn_rank_eq_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW@3 = 1
03)----BoundedWindowAggExec: wdw=[rank() PARTITION BY [window_topn_rank_eq_t.pk] ORDER BY [window_topn_rank_eq_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW: Field { "rank() PARTITION BY [window_topn_rank_eq_t.pk] ORDER BY [window_topn_rank_eq_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW": UInt64 }, frame: RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW], mode=[Sorted]
04)------SortExec: expr=[pk@1 ASC NULLS LAST, val@2 ASC NULLS LAST], preserve_partitioning=[false]
02)--BoundedWindowAggExec: wdw=[rank() PARTITION BY [window_topn_rank_eq_t.pk] ORDER BY [window_topn_rank_eq_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW: Field { "rank() PARTITION BY [window_topn_rank_eq_t.pk] ORDER BY [window_topn_rank_eq_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW": UInt64 }, frame: RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW], mode=[Sorted]
03)----RepartitionExec: partitioning=Hash([pk@1], 4), input_partitions=1, maintains_sort_order=true
04)------PartitionedTopKExec: fn=rank, fetch=1, partition=[pk@1], order=[val@2 ASC NULLS LAST]
05)--------DataSourceExec: partitions=1, partition_sizes=[1]

statement ok
Expand Down
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