adapter: Prevent enable_variadic_left_join from firing on cross-joins#36640
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mgree wants to merge 3 commits into
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adapter: Prevent enable_variadic_left_join from firing on cross-joins#36640mgree wants to merge 3 commits into
enable_variadic_left_join from firing on cross-joins#36640mgree wants to merge 3 commits into
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May 21, 2026
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I added an extra test that fails:
--- test/sqllogictest/variadic_outer_join.slt
2026-05-21T01:56:57.225736Z ERROR mz_transform: caught a panic during query optimization: type error in transient query:
In the MIR term:
Project (#0, #1)
Union
Get l1
Constant
- (null)
projection of non-existant columns [0, 1] from type (r_int32?)
With
cte l0 =
Constant
- ()
Return
Project (#0, #3, #1, #4)
With
cte l1 =
CrossJoin
Get l0
Get u1
cte l3 =
Project (#0..=#3)
Map (true)
With
cte l2 =
CrossJoin
Get l0
Get u2
Return
Get l2
cte l6 =
Project (#0, #1)
Map (true)
With
cte l5 =
CrossJoin
Get l0
Get u3
Return
Get l5
cte l4 =
Union
Filter (#1) IS NOT NULL AND (#2) IS NOT NULL
Get l3
Project (#2, #1, #0, #5)
Map (null, null, null, null)
Threshold
Union
Negate
Project (#2, #1)
Filter (#1) IS NOT NULL AND (#2) IS NOT NULL
Get l3
Distinct project=[#0, #1]
Project (#0, #1)
Union
Get l1
Constant
- (null)
cte l7 =
Union
Filter (#0) IS NOT NULL
Get l6
Project (#0, #2)
Map (null, null)
Threshold
Union
Negate
Project (#0)
Filter (#0) IS NOT NULL
Get l6
Distinct project=[#0]
Project (#0)
Union
Get l1
Constant
- (null)
Return
Project (#0..=#3, #6)
Map (case when (#5) IS NULL then null else #4 end)
Filter ((#0 = #4) OR ((#0) IS NULL AND (#4) IS NULL))
Project (#0..=#5)
CrossJoin
Project (#0, #5..=#7)
Map (case when (#4) IS NULL then null else #1 end, case when (#4) IS NULL then null else #2 end, case when (#4) IS NULL then null else #3 end)
Filter ((#0 = #3) OR ((#0) IS NULL AND (#3) IS NULL)) AND ((#1 = #2) OR ((#1) IS NULL AND (#2) IS NULL))
Project (#0..=#4)
CrossJoin
Get l1
Get l4
Get l7
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
PlanFailure:test/sqllogictest/variadic_outer_join.slt:197:
db error: ERROR: internal error: internal error in optimizer: internal transform error: unexpected panic during query optimization: type error in transient query:
In the MIR term:
Project (#0, #1)
Union
Get l1
Constant
- (null)
projection of non-existant columns [0, 1] from type (r_int32?)
With
cte l0 =
Constant
- ()
Return
Project (#0, #3, #1, #4)
With
cte l1 =
CrossJoin
Get l0
Get u1
cte l3 =
Project (#0..=#3)
Map (true)
With
cte l2 =
CrossJoin
Get l0
Get u2
Return
Get l2
cte l6 =
Project (#0, #1)
Map (true)
With
cte l5 =
CrossJoin
Get l0
Get u3
Return
Get l5
cte l4 =
Union
Filter (#1) IS NOT NULL AND (#2) IS NOT NULL
Get l3
Project (#2, #1, #0, #5)
Map (null, null, null, null)
Threshold
Union
Negate
Project (#2, #1)
Filter (#1) IS NOT NULL AND (#2) IS NOT NULL
Get l3
Distinct project=[#0, #1]
Project (#0, #1)
Union
Get l1
Constant
- (null)
cte l7 =
Union
Filter (#0) IS NOT NULL
Get l6
Project (#0, #2)
Map (null, null)
Threshold
Union
Negate
Project (#0)
Filter (#0) IS NOT NULL
Get l6
Distinct project=[#0]
Project (#0)
Union
Get l1
Constant
- (null)
Return
Project (#0..=#3, #6)
Map (case when (#5) IS NULL then null else #4 end)
Filter ((#0 = #4) OR ((#0) IS NULL AND (#4) IS NULL))
Project (#0..=#5)
CrossJoin
Project (#0, #5..=#7)
Map (case when (#4) IS NULL then null else #1 end, case when (#4) IS NULL then null else #2 end, case when (#4) IS NULL then null else #3 end)
Filter ((#0 = #3) OR ((#0) IS NULL AND (#3) IS NULL)) AND ((#1 = #2) OR ((#1) IS NULL AND (#2) IS NULL))
Project (#0..=#4)
CrossJoin
Get l1
Get l4
Get l7
----
FAIL: plan-failure=1 success=12 total=13
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Motivation
Fixes https://linear.app/materializeinc/issue/SQL-286/enable-variadic-left-join-lowering-causes-wrong-results.
Description
When trying to apply the variadic left join lowering (
attempt_left_join_magic), we try to identify a column in the right-hand side of theLEFT JOINthat is equated to abound_inputin the left-hand side. The code correctly checked that the right-hand side was in the right relation, but only ensured that the left-hand side was uncorrelated. When presented with a cross join (as in the original bug report,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, we must plana LEFT JOIN b ON b.x = b.yas a cross-join), we will attempt the lowering---when in fact we should not.The fix is simple: make sure that the left column is actually in the left-hand side.
Verification
Repro from the bug report went red to green. No need for other SLT rewrites (i.e., doesn't break existing examples).