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fix: Fix bug with structurally equal correlated subqueries #22313

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fix: Fix bug with structurally equal correlated subqueries #22313

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8b1cc40
fix: Structurally equal corr subqueries were misevaluated
neilconway May 17, 2026
92cfc9b
Map aliases to expr indexes directly
neilconway May 19, 2026
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33 changes: 14 additions & 19 deletions datafusion/optimizer/src/scalar_subquery_to_join.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -153,20 +153,17 @@ impl OptimizerRule for ScalarSubqueryToJoin {
}

let mut all_subqueries = vec![];
#[allow(clippy::allow_attributes, clippy::mutable_key_type)]
// Expr contains Arc with interior mutability but is intentionally used as hash key
let mut expr_to_rewrite_expr_map = HashMap::new();
#[allow(clippy::allow_attributes, clippy::mutable_key_type)]
// Expr contains Arc with interior mutability but is intentionally used as hash key
let mut subquery_to_expr_map = HashMap::new();
for expr in projection.expr.iter() {
let (subqueries, rewrite_exprs) =
let mut alias_to_index: HashMap<String, usize> = HashMap::new();
let mut rewrite_exprs: Vec<Expr> =
Vec::with_capacity(projection.expr.len());
for (idx, expr) in projection.expr.iter().enumerate() {
let (subqueries, rewrite_expr) =
self.extract_subquery_exprs(expr, config.alias_generator())?;
for (subquery, _) in &subqueries {
subquery_to_expr_map.insert(subquery.clone(), expr.clone());
for (_, alias) in &subqueries {
alias_to_index.insert(alias.clone(), idx);
}
all_subqueries.extend(subqueries);
expr_to_rewrite_expr_map.insert(expr, rewrite_exprs);
rewrite_exprs.push(rewrite_expr);
}
assert_or_internal_err!(
!all_subqueries.is_empty(),
Expand All @@ -180,10 +177,9 @@ impl OptimizerRule for ScalarSubqueryToJoin {
{
cur_input = optimized_subquery;
if !expr_check_map.is_empty()
&& let Some(expr) = subquery_to_expr_map.get(&subquery)
&& let Some(rewrite_expr) = expr_to_rewrite_expr_map.get(expr)
&& let Some(&idx) = alias_to_index.get(&alias)
{
let new_expr = rewrite_expr
let new_expr = rewrite_exprs[idx]
.clone()
.transform_up(|expr| {
// replace column references with entry in map, if it exists
Expand All @@ -197,7 +193,7 @@ impl OptimizerRule for ScalarSubqueryToJoin {
}
})
.data()?;
expr_to_rewrite_expr_map.insert(expr, new_expr);
rewrite_exprs[idx] = new_expr;
}
} else {
// if we can't handle all of the subqueries then bail for now
Expand All @@ -206,14 +202,13 @@ impl OptimizerRule for ScalarSubqueryToJoin {
}

let mut proj_exprs = vec![];
for expr in projection.expr.iter() {
for (expr, new_expr) in projection.expr.iter().zip(rewrite_exprs) {
let old_expr_name = expr.schema_name().to_string();
let new_expr = expr_to_rewrite_expr_map.get(expr).unwrap();
let new_expr_name = new_expr.schema_name().to_string();
if new_expr_name != old_expr_name {
proj_exprs.push(new_expr.clone().alias(old_expr_name))
proj_exprs.push(new_expr.alias(old_expr_name))
} else {
proj_exprs.push(new_expr.clone());
proj_exprs.push(new_expr);
}
}
let new_plan = LogicalPlanBuilder::from(cur_input)
Expand Down
16 changes: 16 additions & 0 deletions datafusion/sqllogictest/test_files/subquery.slt
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Original file line number Diff line number Diff line change
Expand Up @@ -851,6 +851,22 @@ SELECT t1_id, (SELECT count(*) FROM t2 WHERE t2.t2_int = t1.t1_int) from t1
44 0


#correlated_scalar_subquery_count_agg_duplicated_in_projection
# Two structurally identical correlated COUNT subqueries in the same
# projection must each receive the count-bug compensation, so unmatched
# outer rows produce 0 (not NULL) on both sides.
query III rowsort
SELECT
t1_id,
(SELECT count(*) FROM t2 WHERE t2.t2_int = t1.t1_int) + 1 AS a,
(SELECT count(*) FROM t2 WHERE t2.t2_int = t1.t1_int) + 2 AS b
FROM t1
----
11 2 3
22 1 2
33 4 5
44 1 2

#correlated_scalar_subquery_count_agg2
query TT
explain SELECT t1_id, (SELECT count(*) FROM t2 WHERE t2.t2_int = t1.t1_int) as cnt from t1
Expand Down
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