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fix: Derive Substrait intersection nullability from every input #25091

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fix: Derive Substrait intersection nullability from every input #25091

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88 changes: 80 additions & 8 deletions datafusion/substrait/src/logical_plan/consumer/rel/set_rel.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,8 +16,9 @@
// under the License.

use crate::logical_plan::consumer::SubstraitConsumer;
use datafusion::common::{not_impl_err, substrait_err};
use datafusion::logical_expr::{LogicalPlan, LogicalPlanBuilder};
use datafusion::common::{DFSchema, not_impl_err, substrait_err};
use datafusion::logical_expr::{Expr, LogicalPlan, LogicalPlanBuilder, Projection};
use std::sync::Arc;
use substrait::proto::set_rel::SetOp;
use substrait::proto::{Rel, SetRel};

Expand All @@ -31,7 +32,7 @@ pub async fn from_set_rel(
match set.op() {
SetOp::UnionAll => union_rels(consumer, &set.inputs, true).await,
SetOp::UnionDistinct => union_rels(consumer, &set.inputs, false).await,
SetOp::IntersectionPrimary => LogicalPlanBuilder::intersect(
SetOp::IntersectionPrimary => intersect_rel(
consumer.consume_rel(&set.inputs[0]).await?,
union_rels(consumer, &set.inputs[1..], true).await?,
false,
Expand Down Expand Up @@ -77,16 +78,87 @@ async fn intersect_rels(
let mut rel = consumer.consume_rel(&rels[0]).await?;

for input in &rels[1..] {
rel = LogicalPlanBuilder::intersect(
rel,
consumer.consume_rel(input).await?,
is_all,
)?;
rel = intersect_rel(rel, consumer.consume_rel(input).await?, is_all)?;
}

Ok(rel)
}

/// Intersects two relations, giving the result the nullability the Substrait
/// [Set Operation rules] prescribe.
///
/// [`LogicalPlanBuilder::intersect`] compiles an intersection into a left semi
/// join, so on its own the result keeps the left input's nullability. The join
/// matches nulls with nulls, so a left row holding a null in some field only
/// survives when the right input holds a null there too. A field is therefore
/// nullable in the result only when it is nullable in *both* inputs.
///
/// Applied to each step of a chain, that gives the spec's rule for the multiset
/// intersections - a field is required when any input requires it. For
/// `INTERSECTION_PRIMARY` the right side is the union of the secondary inputs,
/// whose field is nullable exactly when some secondary input makes it nullable,
/// so the same rule yields "nullable in the primary input and in at least one
/// secondary input".
///
/// [Set Operation rules]: https://substrait.io/relations/logical_relations/#set-operation
fn intersect_rel(
left: LogicalPlan,
right: LogicalPlan,
is_all: bool,
) -> datafusion::common::Result<LogicalPlan> {
let right_nullability: Vec<bool> = right
.schema()
.fields()
.iter()
.map(|field| field.is_nullable())
.collect();

let plan = LogicalPlanBuilder::intersect(left, right, is_all)?;

// `intersect` has already checked that both sides have the same width.
let narrowed: Vec<bool> = plan
.schema()
.fields()
.iter()
.zip(&right_nullability)
.map(|(field, right_nullable)| field.is_nullable() && !right_nullable)
.collect();

if !narrowed.contains(&true) {
return Ok(plan);
}

let qualified_fields = plan
.schema()
.iter()
.zip(&narrowed)
.map(|((qualifier, field), narrow)| {
let field = if *narrow {
Arc::new(field.as_ref().clone().with_nullable(false))
} else {
Arc::clone(field)
};
(qualifier.cloned(), field)
})
.collect();
let schema = Arc::new(DFSchema::new_with_metadata(
qualified_fields,
plan.schema().metadata().clone(),
)?);

let exprs = plan
.schema()
.columns()
.into_iter()
.map(Expr::Column)
.collect();
Ok(LogicalPlan::Projection(Projection::try_new_with_schema(
exprs,
Arc::new(plan),
schema,
)?))
}

async fn except_rels(
consumer: &impl SubstraitConsumer,
rels: &[Rel],
Expand Down
44 changes: 44 additions & 0 deletions datafusion/substrait/tests/cases/logical_plans.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -229,6 +229,50 @@ mod tests {
Ok(())
}

#[tokio::test]
async fn intersect_nullability() -> Result<()> {
// Substrait's set operation rules derive an intersection's nullability from
// every input, not only the primary one. Each plan below intersects three
// tables carrying the same four columns, with these nullabilities
// (`?` marks a nullable column):
//
// primary a? b? c? d?
// secondary a b c? d?
// secondary a b? c d?
for (file, expected) in [
// Nullable in the primary input and in at least one secondary input.
("intersect_primary_mixed_nullability", "a, b?, c?, d?"),
// Required as soon as any input requires it.
("intersect_multiset_mixed_nullability", "a, b, c, d?"),
("intersect_multiset_all_mixed_nullability", "a, b, c, d?"),
] {
let proto_plan =
read_json(&format!("tests/testdata/test_plans/{file}.substrait.json"));
let ctx = add_plan_schemas_to_ctx(SessionContext::new(), &proto_plan)?;
let plan = from_substrait_plan(&ctx.state(), &proto_plan).await?;

let nullability = plan
.schema()
.fields()
.iter()
.map(|field| {
format!(
"{}{}",
field.name(),
if field.is_nullable() { "?" } else { "" }
)
})
.collect::<Vec<_>>()
.join(", ");
assert_eq!(nullability, expected, "nullability of {file}");

// Trigger execution to ensure plan validity
DataFrame::new(ctx.state(), plan).show().await?;
}

Ok(())
}

#[tokio::test]
async fn multilayer_aggregate() -> Result<()> {
let proto_plan =
Expand Down
160 changes: 160 additions & 0 deletions ...bstrait/tests/testdata/test_plans/intersect_multiset_all_mixed_nullability.substrait.json
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Original file line number Diff line number Diff line change
@@ -0,0 +1,160 @@
{
"relations": [
{
"root": {
"input": {
"set": {
"inputs": [
{
"read": {
"common": {
"direct": {}
},
"baseSchema": {
"names": [
"a",
"b",
"c",
"d"
],
"struct": {
"types": [
{
"i64": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"i64": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"i64": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"i64": {
"nullability": "NULLABILITY_NULLABLE"
}
}
],
"nullability": "NULLABILITY_REQUIRED"
}
},
"namedTable": {
"names": [
"data"
]
}
}
},
{
"read": {
"common": {
"direct": {}
},
"baseSchema": {
"names": [
"a",
"b",
"c",
"d"
],
"struct": {
"types": [
{
"i64": {
"nullability": "NULLABILITY_REQUIRED"
}
},
{
"i64": {
"nullability": "NULLABILITY_REQUIRED"
}
},
{
"i64": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"i64": {
"nullability": "NULLABILITY_NULLABLE"
}
}
],
"nullability": "NULLABILITY_REQUIRED"
}
},
"namedTable": {
"names": [
"data2"
]
}
}
},
{
"read": {
"common": {
"direct": {}
},
"baseSchema": {
"names": [
"a",
"b",
"c",
"d"
],
"struct": {
"types": [
{
"i64": {
"nullability": "NULLABILITY_REQUIRED"
}
},
{
"i64": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"i64": {
"nullability": "NULLABILITY_REQUIRED"
}
},
{
"i64": {
"nullability": "NULLABILITY_NULLABLE"
}
}
],
"nullability": "NULLABILITY_REQUIRED"
}
},
"namedTable": {
"names": [
"data3"
]
}
}
}
],
"op": "SET_OP_INTERSECTION_MULTISET_ALL"
}
},
"names": [
"a",
"b",
"c",
"d"
]
}
}
],
"version": {
"minorNumber": 54,
"producer": "datafusion-test"
}
}
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