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fix: Correct join cardinality estimation for semi and anti joins with disjoint column ranges #22674

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fix: Correct join cardinality estimation for semi and anti joins with disjoint column ranges #22674

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115 changes: 85 additions & 30 deletions datafusion/physical-plan/src/joins/utils.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -475,7 +475,7 @@ fn estimate_join_cardinality(
right_stats: Statistics,
on: &JoinOn,
) -> Option<PartialJoinStatistics> {
let (left_col_stats, right_col_stats) = on
let (left_key_stats, right_key_stats) = on
.iter()
.map(|(left, right)| {
match (
Expand All @@ -500,12 +500,12 @@ fn estimate_join_cardinality(
Statistics {
num_rows: left_stats.num_rows,
total_byte_size: Precision::Absent,
column_statistics: left_col_stats,
column_statistics: left_key_stats,
},
Statistics {
num_rows: right_stats.num_rows,
total_byte_size: Precision::Absent,
column_statistics: right_col_stats,
column_statistics: right_key_stats,
},
)?;

Expand Down Expand Up @@ -545,38 +545,49 @@ fn estimate_join_cardinality(
let is_left = matches!(join_type, JoinType::LeftSemi | JoinType::LeftAnti);
let is_anti = matches!(join_type, JoinType::LeftAnti | JoinType::RightAnti);

let ((outer_stats, inner_stats), (outer_col_stats, inner_col_stats)) =
if is_left {
(
(&left_stats, &right_stats),
(&left_col_stats, &right_col_stats),
)
} else {
(
(&right_stats, &left_stats),
(&right_col_stats, &left_col_stats),
)
};
let (outer_stats, inner_stats, outer_key_stats, inner_key_stats) = if is_left
{
(&left_stats, &right_stats, &left_key_stats, &right_key_stats)
} else {
(&right_stats, &left_stats, &right_key_stats, &left_key_stats)
};

let outer_rows = *outer_stats.num_rows.get_value()?;

let cardinality =
if estimate_disjoint_inputs(outer_stats, inner_stats).is_some() {
// Disjoint inputs: semi produces 0, anti keeps all rows.
if is_anti { outer_rows } else { 0 }
let outer_join_key_stats = Statistics {
num_rows: outer_stats.num_rows,
total_byte_size: Precision::Absent,
column_statistics: outer_key_stats.clone(),
};
let inner_join_key_stats = Statistics {
num_rows: inner_stats.num_rows,
total_byte_size: Precision::Absent,
column_statistics: inner_key_stats.clone(),
};

let semi_cardinality =
if estimate_disjoint_inputs(&outer_join_key_stats, &inner_join_key_stats)
.is_some()
{
// If join keys are disjoint, no rows will match
Some(0)
} else {
match estimate_semi_join_cardinality(
estimate_semi_join_cardinality(
&outer_stats.num_rows,
&inner_stats.num_rows,
outer_col_stats,
inner_col_stats,
) {
Some(semi) if is_anti => outer_rows.saturating_sub(semi),
Some(semi) => semi,
None => outer_rows,
}
outer_key_stats,
inner_key_stats,
)
};

// Semi joins keep the matching rows; anti joins keep the rest. When no
// estimate is available, conservatively assume all outer rows pass.
let cardinality = match (semi_cardinality, is_anti) {
(Some(semi), true) => outer_rows.saturating_sub(semi),
(Some(semi), false) => semi,
(None, _) => outer_rows,
};

let outer_stats = if is_left { left_stats } else { right_stats };
Some(PartialJoinStatistics {
num_rows: cardinality,
Expand Down Expand Up @@ -759,8 +770,8 @@ fn estimate_disjoint_inputs(
fn estimate_semi_join_cardinality(
outer_num_rows: &Precision<usize>,
inner_num_rows: &Precision<usize>,
outer_col_stats: &[ColumnStatistics],
inner_col_stats: &[ColumnStatistics],
outer_key_stats: &[ColumnStatistics],
inner_key_stats: &[ColumnStatistics],
) -> Option<usize> {
let outer_rows = *outer_num_rows.get_value()?;
if outer_rows == 0 {
Expand All @@ -774,7 +785,7 @@ fn estimate_semi_join_cardinality(
let mut selectivity = 1.0_f64;
let mut has_selectivity_estimate = false;

for (outer_stat, inner_stat) in outer_col_stats.iter().zip(inner_col_stats.iter()) {
for (outer_stat, inner_stat) in outer_key_stats.iter().zip(inner_key_stats.iter()) {
let outer_has_stats = outer_stat.distinct_count.get_value().is_some()
|| (outer_stat.min_value.get_value().is_some()
&& outer_stat.max_value.get_value().is_some());
Expand Down Expand Up @@ -3246,6 +3257,50 @@ mod tests {
Ok(())
}

#[test]
fn test_semi_anti_join_disjoint_check_uses_only_join_keys() {
let join_on = vec![(
Arc::new(Column::new("l_key", 0)) as _,
Arc::new(Column::new("r_key", 0)) as _,
)];

// Ranges for the join key overlap; ranges for the other column are disjoint
let left_stats = Statistics {
num_rows: Inexact(50),
total_byte_size: Absent,
column_statistics: vec![
create_column_stats(Inexact(1), Inexact(10), Absent, Absent),
create_column_stats(Inexact(100), Inexact(200), Absent, Absent),
],
};
let right_stats = Statistics {
num_rows: Inexact(10),
total_byte_size: Absent,
column_statistics: vec![
create_column_stats(Inexact(1), Inexact(10), Absent, Absent),
create_column_stats(Inexact(1000), Inexact(2000), Absent, Absent),
],
};

let left_semi = estimate_join_cardinality(
&JoinType::LeftSemi,
left_stats.clone(),
right_stats.clone(),
&join_on,
)
.map(|c| c.num_rows);
assert_eq!(left_semi, Some(50));

let left_anti = estimate_join_cardinality(
&JoinType::LeftAnti,
left_stats,
right_stats,
&join_on,
)
.map(|c| c.num_rows);
assert_eq!(left_anti, Some(0));
}

#[test]
fn test_calculate_join_output_ordering() -> Result<()> {
let left_ordering = LexOrdering::new(vec![
Expand Down
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