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Do not convert full outer joins to cross joins #3274

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Merged
merged 1 commit into from
Oct 20, 2025
Merged

Do not convert full outer joins to cross joins #3274

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9 changes: 9 additions & 0 deletions enginetest/join_op_tests.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2181,6 +2181,7 @@ WHERE
},
{
// https://github.com/dolthub/dolt/issues/9782
// https://github.com/dolthub/dolt/issues/9973
name: "joining with subquery on empty table",
setup: [][]string{
{
Expand All @@ -2205,6 +2206,14 @@ WHERE
Query: "SELECT t.c FROM (SELECT t.c FROM t WHERE FALSE) AS subq NATURAL RIGHT JOIN t;",
Expected: []sql.Row{{1}},
},
{
Query: "SELECT t.c FROM t FULL OUTER JOIN (SELECT t.c FROM t WHERE FALSE) AS subq ON TRUE;",
Expected: []sql.Row{{1}},
},
{
Query: "SELECT t.c FROM (SELECT t.c FROM t WHERE FALSE) AS subq FULL OUTER JOIN t ON TRUE;",
Expected: []sql.Row{{1}},
},
},
},
{
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11 changes: 7 additions & 4 deletions sql/planbuilder/from.go
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Original file line number Diff line number Diff line change
Expand Up @@ -79,10 +79,13 @@ func (b *Builder) isUsingJoin(te *ast.JoinTableExpr) bool {
}

func (b *Builder) canConvertToCrossJoin(te *ast.JoinTableExpr) bool {
return !strings.EqualFold(te.Join, ast.LeftJoinStr) &&
!strings.EqualFold(te.Join, ast.RightJoinStr) &&
(te.Condition.On == nil || te.Condition.On == ast.BoolVal(true)) &&
te.Condition.Using == nil
switch te.Join {
case ast.LeftJoinStr, ast.RightJoinStr, ast.FullOuterJoinStr:
return false
default:
return (te.Condition.On == nil || te.Condition.On == ast.BoolVal(true)) &&
te.Condition.Using == nil
}
}

func (b *Builder) buildJoin(inScope *scope, te *ast.JoinTableExpr) (outScope *scope) {
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