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fix: avoid eliminating the left child of union in RuleEliminateUnion #16584

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merged 1 commit into from
Oct 10, 2024
Merged

fix: avoid eliminating the left child of union in RuleEliminateUnion #16584

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6 changes: 3 additions & 3 deletions src/query/sql/src/planner/optimizer/rule/rewrite/rule_eliminate_union.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -75,6 +75,9 @@ impl Rule for RuleEliminateUnion {
let left_child = s_expr.child(0)?;
let right_child = s_expr.child(1)?;

// If left child is empty, we won't eliminate it
// Because the schema of the union is from left child, and the union node's parent relies on the schema
// And the parent's schema has been binded during the binder phase.
if Self::is_empty_scan(left_child)? && Self::is_empty_scan(right_child)? {
// If both children are empty, replace with EmptyResultScan
let union_output_columns = union
Expand All @@ -96,9 +99,6 @@ impl Rule for RuleEliminateUnion {
);
let result = SExpr::create_leaf(Arc::new(RelOperator::ConstantTableScan(empty_scan)));
state.add_result(result);
} else if Self::is_empty_scan(left_child)? {
// If left child is empty, use right child
state.add_result(right_child.clone());
} else if Self::is_empty_scan(right_child)? {
// If right child is empty, use left child
state.add_result(left_child.clone());
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24 changes: 14 additions & 10 deletions tests/sqllogictests/suites/mode/standalone/explain/union.test
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Expand Up @@ -240,16 +240,20 @@ query T
----
explain select * from t1 where t1.a < 0 union all select * from t2 ;
----
TableScan
├── table: default.default.t2
├── output columns: []
├── read rows: 10000
├── read size: 0
├── partitions total: 1
├── partitions scanned: 1
├── pruning stats: [segments: <range pruning: 1 to 1>, blocks: <range pruning: 1 to 1>]
├── push downs: [filters: [], limit: NONE]
└── estimated rows: 10000.00
UnionAll
├── output columns: [t1.a (#0)]
├── estimated rows: 10000.00
├── EmptyResultScan
└── TableScan
├── table: default.default.t2
├── output columns: [b (#1)]
├── read rows: 10000
├── read size: 10.59 KiB
├── partitions total: 1
├── partitions scanned: 1
├── pruning stats: [segments: <range pruning: 1 to 1>, blocks: <range pruning: 1 to 1>]
├── push downs: [filters: [], limit: NONE]
└── estimated rows: 10000.00


query T
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13 changes: 13 additions & 0 deletions tests/sqllogictests/suites/query/union.test
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Expand Up @@ -323,3 +323,16 @@ query I
select * from numbers(100) union all select * from numbers(100) ignore_result;
----

statement ok
create or replace table t1 (test bigint);

statement ok
insert into t1 values(1), (0);

query I
WITH cte1 AS ( SELECT t1.test FROM t1 WHERE t1.test = 0 ) ,cte2 AS ( SELECT cte1.test FROM cte1 WHERE cte1.test = 1 UNION ALL SELECT cte1.test FROM cte1 WHERE cte1.test = 0 ) SELECT * FROM cte2;
----
0

statement ok
drop table t1;
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