zhuqi-lucas commented on code in PR #14245:
URL: https://github.com/apache/datafusion/pull/14245#discussion_r1929652858
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datafusion/sqllogictest/test_files/joins.slt:
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@@ -4247,8 +4247,10 @@ logical_plan
physical_plan
01)CoalesceBatchesExec: target_batch_size=3, fetch=2
02)--HashJoinExec: mode=CollectLeft, join_type=Full, on=[(c1@0, c1@0)]
-03)----MemoryExec: partitions=1, partition_sizes=[1]
-04)----MemoryExec: partitions=1, partition_sizes=[1]
+03)----GlobalLimitExec: skip=0, fetch=2
Review Comment:
Hi @alamb :
I looked into the code about the push down for join:
```rust
/// Adds a limit to the inputs of a join, if possible
fn push_down_join(mut join: Join, limit: usize) -> Transformed<Join> {
use JoinType::*;
fn is_no_join_condition(join: &Join) -> bool {
join.on.is_empty() && join.filter.is_none()
}
let (left_limit, right_limit) = if is_no_join_condition(&join) {
match join.join_type {
Left | Right | Full | Inner => (Some(limit), Some(limit)),
LeftAnti | LeftSemi | LeftMark => (Some(limit), None),
RightAnti | RightSemi => (None, Some(limit)),
}
} else {
match join.join_type {
Left => (Some(limit), None),
Right => (None, Some(limit)),
Full => (Some(limit), Some(limit)),
_ => (None, None),
}
};
if left_limit.is_none() && right_limit.is_none() {
return Transformed::no(join);
}
if let Some(limit) = left_limit {
join.left = make_arc_limit(0, limit, join.left);
}
if let Some(limit) = right_limit {
join.right = make_arc_limit(0, limit, join.right);
}
Transformed::yes(join)
}
```
I think it's safe we just want to limit any result, we don't care about
which line to return for the optimization.
If we want to get the accurate limit same with not limit, i think we need to
remove those push down join optimization?
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