zhuqi-lucas commented on code in PR #16641:
URL: https://github.com/apache/datafusion/pull/16641#discussion_r2179151489
##########
datafusion/physical-optimizer/src/enforce_sorting/sort_pushdown.rs:
##########
@@ -668,6 +668,15 @@ fn handle_hash_join(
plan: &HashJoinExec,
parent_required: OrderingRequirements,
) -> Result<Option<Vec<Option<OrderingRequirements>>>> {
+ // Anti-joins (LeftAnti or RightAnti) do not preserve meaningful input
order,
+ // so sorting beforehand cannot be relied on. Bail out early for both
flavors:
+ match plan.join_type() {
+ JoinType::LeftAnti | JoinType::RightAnti => {
+ return Ok(None);
+ }
+ _ => {}
+ }
Review Comment:
Updated, i checked the code, we will not push down limit for anti join:
https://github.com/apache/datafusion/blob/25c2a079fc1baacc038e304cb2bcae671338c2d8/datafusion/optimizer/src/push_down_limit.rs#L256
And example:
```rust
CREATE TABLE t1 AS VALUES
(1, 'a'),
(2, 'b'),
(3, 'c');
0 row(s) fetched.
Elapsed 0.004 seconds.
> CREATE TABLE t2 AS VALUES
(1, 'a');
0 row(s) fetched.
Elapsed 0.003 seconds.
> -- LIMIT potentially pushed down (depends on optimizer)
SELECT * FROM t1 LEFT ANTI JOIN t2 ON t1.column1 = t2.column1 LIMIT 2;
+---------+---------+
| column1 | column2 |
+---------+---------+
| 2 | b |
| 3 | c |
+---------+---------+
2 row(s) fetched.
Elapsed 0.003 seconds.
> -- LIMIT applied after anti join (expected)
SELECT * FROM (
SELECT * FROM t1 LEFT ANTI JOIN t2 ON t1.column1 = t2.column1
) LIMIT 2;
+---------+---------+
| column1 | column2 |
+---------+---------+
| 2 | b |
| 3 | c |
+---------+---------+
2 row(s) fetched.
Elapsed 0.002 seconds.
> EXPLAIN SELECT * FROM t1 LEFT ANTI JOIN t2 ON t1.column1 = t2.column1
LIMIT 2;
+---------------+------------------------------------------------------------+
| plan_type | plan
|
+---------------+------------------------------------------------------------+
| physical_plan | ┌───────────────────────────┐
|
| | │ CoalesceBatchesExec │
|
| | │ -------------------- │
|
| | │ limit: 2 │
|
| | │ │
|
| | │ target_batch_size: │
|
| | │ 8192 │
|
| | └─────────────┬─────────────┘
|
| | ┌─────────────┴─────────────┐
|
| | │ HashJoinExec │
|
| | │ -------------------- │
|
| | │ join_type: RightAnti │
|
| | │ ├──────────────┐
|
| | │ on: │ │
|
| | │ (column1 = column1) │ │
|
| | └─────────────┬─────────────┘ │
|
| | ┌─────────────┴─────────────┐┌─────────────┴─────────────┐
|
| | │ DataSourceExec ││ DataSourceExec │
|
| | │ -------------------- ││ -------------------- │
|
| | │ bytes: 1336 ││ bytes: 1336 │
|
| | │ format: memory ││ format: memory │
|
| | │ rows: 1 ││ rows: 1 │
|
| | └───────────────────────────┘└───────────────────────────┘
|
| |
|
+---------------+------------------------------------------------------------+
1 row(s) fetched.
Elapsed 0.003 seconds.
```
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