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adapter: Prevent enable_variadic_left_join from firing on cross-joins #36640

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adapter: Prevent enable_variadic_left_join from firing on cross-joins #36640

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08548ff
test from bug report, enriched with plans
mgree May 20, 2026
40fc52d
ensure the bound input is actually in the input
mgree May 20, 2026
2c7486f
slt: Add additional test case
def- May 21, 2026
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5 changes: 3 additions & 2 deletions src/sql/src/plan/lowering/variadic_left.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -196,8 +196,9 @@ pub(crate) fn attempt_left_join_magic(
inc_metrics("voj_5");
return Ok(None);
}
// Only columns not from the outer scope introduce bindings.
if left >= oa {
// Only columns not from the outer scope introduce bindings (`oa <= left`)
// And `left` needs to be a column in the left relation (`left < oa + ba`)
if oa <= left && left < oa + ba {
if let Some(bound) = bound_input {
// If left references come from different inputs, bail out.
if bound_to[left] != bound {
Expand Down
200 changes: 200 additions & 0 deletions test/sqllogictest/variadic_outer_join.slt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,200 @@
# Copyright Materialize, Inc. and contributors. All rights reserved.
#
# Use of this software is governed by the Business Source License
# included in the LICENSE file at the root of this repository.
#
# As of the Change Date specified in that file, in accordance with
# the Business Source License, use of this software will be governed
# by the Apache License, Version 2.0.

mode cockroach

statement ok
CREATE TABLE a (k int)

statement ok
CREATE TABLE b (x int, y int, k int)

statement ok
CREATE TABLE c (k int)

statement ok
INSERT INTO a VALUES (1)

# Only (5, 5, 100) satisfies the b.x = b.y filter.
statement ok
INSERT INTO b VALUES (5, 5, 100), (3, 7, 200)

statement ok
INSERT INTO c VALUES (100)

# Baseline: with the variadic LEFT JOIN lowering disabled, the generic
# outer-join lowering classifies `b.x = b.y` as a right-local filter and
# produces the correct single-row result.
simple conn=mz_system,user=mz_system
ALTER SYSTEM SET enable_variadic_left_join_lowering TO false
----
COMPLETE 0

query T multiline
EXPLAIN OPTIMIZED PLAN FOR
SELECT a.k, b.x, b.y, b.k, c.k
FROM (a LEFT JOIN b ON b.x = b.y) LEFT JOIN c ON b.k = c.k
----
Explained Query:
With
cte l0 =
CrossJoin type=differential
ArrangeBy keys=[[]]
ReadStorage materialize.public.a
ArrangeBy keys=[[]]
Filter (#0 = #1)
ReadStorage materialize.public.b
cte l1 =
Union
Get l0
Project (#0, #2..=#4)
Map (null, null, null)
Join on=(#0 = #1) type=differential
ArrangeBy keys=[[#0]]
Union
Negate
Distinct project=[#0]
Project (#0)
Get l0
Distinct project=[#0]
ReadStorage materialize.public.a
ArrangeBy keys=[[#0]]
ReadStorage materialize.public.a
cte l2 =
ArrangeBy keys=[[#3{k}]]
Filter (#3{k}) IS NOT NULL
Get l1
cte l3 =
Project (#0..=#3)
Join on=(#3{k} = #4{k}) type=differential
Get l2
ArrangeBy keys=[[#0{k}]]
Filter (#0{k}) IS NOT NULL
ReadStorage materialize.public.c
Return
Union
Map (null)
Union
Negate
Project (#0..=#3)
Join on=(#3{k} = #4) type=differential
Get l2
ArrangeBy keys=[[#0]]
Distinct project=[#0]
Project (#3)
Get l3
Get l1
Project (#0..=#3, #3)
Get l3

Source materialize.public.a
Source materialize.public.b
filter=((#0 = #1))
Source materialize.public.c
filter=((#0{k}) IS NOT NULL)

Target cluster: quickstart

EOF

query IIIII rowsort
SELECT a.k, b.x, b.y, b.k, c.k
FROM (a LEFT JOIN b ON b.x = b.y) LEFT JOIN c ON b.k = c.k
----
1 5 5 100 100

# Re-enable the variadic lowering (the system default) and re-run the
# same query. The expected result is unchanged.
# But we have observed a buggy extra NULL-enriched row (in comments below)

simple conn=mz_system,user=mz_system
ALTER SYSTEM SET enable_variadic_left_join_lowering TO true
----
COMPLETE 0

query T multiline
EXPLAIN OPTIMIZED PLAN FOR
SELECT a.k, b.x, b.y, b.k, c.k
FROM (a LEFT JOIN b ON b.x = b.y) LEFT JOIN c ON b.k = c.k
----
Explained Query:
With
cte l0 =
CrossJoin type=differential
ArrangeBy keys=[[]]
ReadStorage materialize.public.a
ArrangeBy keys=[[]]
Filter (#0 = #1)
ReadStorage materialize.public.b
cte l1 =
Union
Get l0
Project (#0, #2..=#4)
Map (null, null, null)
Join on=(#0 = #1) type=differential
ArrangeBy keys=[[#0]]
Union
Negate
Distinct project=[#0]
Project (#0)
Get l0
Distinct project=[#0]
ReadStorage materialize.public.a
ArrangeBy keys=[[#0]]
ReadStorage materialize.public.a
cte l2 =
ArrangeBy keys=[[#3{k}]]
Filter (#3{k}) IS NOT NULL
Get l1
cte l3 =
Project (#0..=#3)
Join on=(#3{k} = #4{k}) type=differential
Get l2
ArrangeBy keys=[[#0{k}]]
Filter (#0{k}) IS NOT NULL
ReadStorage materialize.public.c
Return
Union
Map (null)
Union
Negate
Project (#0..=#3)
Join on=(#3{k} = #4) type=differential
Get l2
ArrangeBy keys=[[#0]]
Distinct project=[#0]
Project (#3)
Get l3
Get l1
Project (#0..=#3, #3)
Get l3

Source materialize.public.a
Source materialize.public.b
filter=((#0 = #1))
Source materialize.public.c
filter=((#0{k}) IS NOT NULL)

Target cluster: quickstart

EOF

query IIIII rowsort
SELECT a.k, b.x, b.y, b.k, c.k
FROM (a LEFT JOIN b ON b.x = b.y) LEFT JOIN c ON b.k = c.k
----
1 5 5 100 100

# 1 NULL NULL NULL NULL

query IIII rowsort
SELECT a.k, b.k, b.x, c.k
FROM (a LEFT JOIN b ON a.k = b.k AND b.x = b.y) LEFT JOIN c ON a.k = c.k
----
1 NULL NULL NULL
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