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Support equality with one in DF55 WindowTopN safely #127

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69 changes: 57 additions & 12 deletions datafusion/physical-optimizer/src/window_topn.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,7 @@ 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 @@ -108,11 +109,10 @@ use datafusion_physical_plan::windows::{BoundedWindowAggExec, WindowUDFExpr};
/// - The window function is `ROW_NUMBER` or `RANK` (not `DENSE_RANK`)
/// - The window function has a `PARTITION BY` clause (global top-K is
/// already handled by `SortExec` with `fetch`)
/// - For `RANK`: a non-empty `ORDER BY` clause (otherwise all rows tie
/// at rank 1 — the optimization is useless and the boundary-tie storage
/// would be unbounded)
/// - At least one effective `ORDER BY` key remains after removing keys
/// already covered by the partition prefix
/// - 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 @@ -158,6 +158,17 @@ impl WindowTopN {
}
let fn_kind = supported_window_fn(&window_exprs[window_expr_idx])?;

// Pruning rows before the window can change sibling expressions such as
// LEAD. Ranking functions with the same keys only depend on retained rows.
let matched_expr = &window_exprs[window_expr_idx];
if !window_exprs.iter().all(|expr| {
supported_window_fn(expr).is_some()
&& expr.partition_by() == matched_expr.partition_by()
&& expr.order_by() == matched_expr.order_by()
}) {
return None;
}

// Step 5: Validate PARTITION BY / ORDER BY and collect sort keys from the window expr
let partition_by = window_exprs[window_expr_idx].partition_by();
let partition_prefix_len = partition_by.len();
Expand All @@ -168,21 +179,20 @@ impl WindowTopN {
return None;
}

// For RANK: an empty ORDER BY makes every row tie at rank 1 —
// the optimization is degenerate (we'd retain the entire input)
// and tie storage would be unbounded.
let order_by = window_exprs[window_expr_idx].order_by();
if matches!(fn_kind, WindowFnKind::Rank) && order_by.is_empty() {
return None;
}

// Step 6: Build PartitionedTopKExec from the window's partition/order keys
let expr_iterator = partition_by
.iter()
.map(|e| PhysicalSortExpr::new_default(Arc::clone(e)))
.chain(order_by.iter().cloned());
let expr = LexOrdering::new(expr_iterator)?;

// TopK requires an order key beyond the partition prefix. LexOrdering
// can remove redundant ORDER BY keys such as ORDER BY pk.
if expr.len() <= partition_prefix_len {
return None;
}

let partitioned_topk = PartitionedTopKExec::try_new(
Arc::clone(window_exec_typed.input()),
expr,
Expand Down Expand Up @@ -250,13 +260,16 @@ 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 @@ -275,6 +288,7 @@ 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 @@ -288,6 +302,7 @@ 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 @@ -359,3 +374,33 @@ 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);
}
}
}
152 changes: 140 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 @@ -865,30 +865,52 @@ 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 *, 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 @@ -901,9 +923,9 @@ 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 Expand Up @@ -1085,6 +1107,112 @@ set datafusion.execution.batch_size = 1;
statement ok
set datafusion.optimizer.enable_window_topn = true;

# A sibling LEAD needs the row after rn=1; pruning before the window would
# turn next_val into NULL. Keep the regular window plan for this case.
statement ok
CREATE TABLE window_topn_sibling_t (id INT, pk INT, val INT) AS VALUES
(1, 1, 10), (2, 1, 20),
(5, 2, 5), (6, 2, 15),
(9, 3, 50), (10, 3, 75);

query IIIII rowsort
SELECT id, pk, val, rn, next_val FROM (
SELECT *,
ROW_NUMBER() OVER (PARTITION BY pk ORDER BY val) AS rn,
LEAD(val) OVER (PARTITION BY pk ORDER BY val) AS next_val
FROM window_topn_sibling_t
) WHERE rn = 1;
----
1 1 10 1 20
5 2 5 1 15
9 3 50 1 75

query TT
EXPLAIN SELECT * FROM (
SELECT *,
ROW_NUMBER() OVER (PARTITION BY pk ORDER BY val) AS rn,
LEAD(val) OVER (PARTITION BY pk ORDER BY val) AS next_val
FROM window_topn_sibling_t
) WHERE rn = 1;
----
logical_plan
01)Projection: window_topn_sibling_t.id, window_topn_sibling_t.pk, window_topn_sibling_t.val, row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW AS rn, lead(window_topn_sibling_t.val) PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW AS next_val
02)--Filter: row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW = UInt64(1)
03)----WindowAggr: windowExpr=[[row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW, lead(window_topn_sibling_t.val) PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW]]
04)------TableScan: window_topn_sibling_t projection=[id, pk, val]
physical_plan
01)ProjectionExec: expr=[id@0 as id, pk@1 as pk, val@2 as val, row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW@3 as rn, lead(window_topn_sibling_t.val) PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW@4 as next_val]
02)--FilterExec: row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW@3 = 1
03)----RepartitionExec: partitioning=RoundRobinBatch(5), input_partitions=1, maintains_sort_order=true
04)------BoundedWindowAggExec: wdw=[row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW: Field { "row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW": UInt64 }, frame: RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW, lead(window_topn_sibling_t.val) PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW: Field { "lead(window_topn_sibling_t.val) PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.val ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW": nullable Int32 }, frame: RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW], mode=[Sorted]
05)--------SortPreservingMergeExec: [pk@1 ASC NULLS LAST, val@2 ASC NULLS LAST]
06)----------SortExec: expr=[pk@1 ASC NULLS LAST, val@2 ASC NULLS LAST], preserve_partitioning=[true]
07)------------DataSourceExec: partitions=5, partition_sizes=[2, 1, 1, 1, 1]

# Both plans have no effective order key and must avoid PartitionedTopKExec.
query I
SELECT COUNT(*) FROM (
SELECT * FROM (
SELECT *, ROW_NUMBER() OVER (PARTITION BY pk) AS rn
FROM window_topn_sibling_t
) WHERE rn = 1
);
----
3

query I
SELECT COUNT(*) FROM (
SELECT * FROM (
SELECT *, ROW_NUMBER() OVER (PARTITION BY pk ORDER BY pk) AS rn
FROM window_topn_sibling_t
) WHERE rn = 1
);
----
3

query TT
EXPLAIN SELECT * FROM (
SELECT *, ROW_NUMBER() OVER (PARTITION BY pk) AS rn
FROM window_topn_sibling_t
) WHERE rn = 1;
----
logical_plan
01)Projection: window_topn_sibling_t.id, window_topn_sibling_t.pk, window_topn_sibling_t.val, row_number() PARTITION BY [window_topn_sibling_t.pk] ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING AS rn
02)--Filter: row_number() PARTITION BY [window_topn_sibling_t.pk] ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING = UInt64(1)
03)----WindowAggr: windowExpr=[[row_number() PARTITION BY [window_topn_sibling_t.pk] ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING]]
04)------TableScan: window_topn_sibling_t projection=[id, pk, val]
physical_plan
01)ProjectionExec: expr=[id@0 as id, pk@1 as pk, val@2 as val, row_number() PARTITION BY [window_topn_sibling_t.pk] ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING@3 as rn]
02)--FilterExec: row_number() PARTITION BY [window_topn_sibling_t.pk] ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING@3 = 1
03)----RepartitionExec: partitioning=RoundRobinBatch(5), input_partitions=1, maintains_sort_order=true
04)------BoundedWindowAggExec: wdw=[row_number() PARTITION BY [window_topn_sibling_t.pk] ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING: Field { "row_number() PARTITION BY [window_topn_sibling_t.pk] ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING": UInt64 }, frame: ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING], mode=[Sorted]
05)--------SortPreservingMergeExec: [pk@1 ASC NULLS LAST]
06)----------SortExec: expr=[pk@1 ASC NULLS LAST], preserve_partitioning=[true]
07)------------DataSourceExec: partitions=5, partition_sizes=[2, 1, 1, 1, 1]

query TT
EXPLAIN SELECT * FROM (
SELECT *, ROW_NUMBER() OVER (PARTITION BY pk ORDER BY pk) AS rn
FROM window_topn_sibling_t
) WHERE rn = 1;
----
logical_plan
01)Projection: window_topn_sibling_t.id, window_topn_sibling_t.pk, window_topn_sibling_t.val, row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.pk ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW AS rn
02)--Filter: row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.pk ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW = UInt64(1)
03)----WindowAggr: windowExpr=[[row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.pk ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW]]
04)------TableScan: window_topn_sibling_t projection=[id, pk, val]
physical_plan
01)ProjectionExec: expr=[id@0 as id, pk@1 as pk, val@2 as val, row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.pk ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW@3 as rn]
02)--FilterExec: row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.pk ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW@3 = 1
03)----RepartitionExec: partitioning=RoundRobinBatch(5), input_partitions=1, maintains_sort_order=true
04)------BoundedWindowAggExec: wdw=[row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.pk ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW: Field { "row_number() PARTITION BY [window_topn_sibling_t.pk] ORDER BY [window_topn_sibling_t.pk ASC NULLS LAST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW": UInt64 }, frame: RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW], mode=[Sorted]
05)--------SortPreservingMergeExec: [pk@1 ASC NULLS LAST]
06)----------SortExec: expr=[pk@1 ASC NULLS LAST], preserve_partitioning=[true]
07)------------DataSourceExec: partitions=5, partition_sizes=[2, 1, 1, 1, 1]

statement ok
DROP TABLE window_topn_sibling_t;

query TT
EXPLAIN SELECT * FROM (
SELECT c1, c2, ROW_NUMBER() OVER (PARTITION BY c1 ORDER BY c2 DESC) as rn
Expand Down
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