mustafasrepo commented on issue #4943:
URL:
https://github.com/apache/arrow-datafusion/issues/4943#issuecomment-1385360298
I think the reason is that UnionExec doesn't implement `fn
maintains_input_order(&self) -> bool`. But sometimes it maintains_input_order.
If we implement `fn maintains_input_order(&self) -> bool` as below (Taken from
`output_ordering` implementation). I think the problem will be solved.
``` rust
fn maintains_input_order(&self) -> bool {
let first_input_ordering = self.inputs[0].output_ordering();
// If the Union is not partition aware and all the input ordering spec
strictly equal with the first_input_ordering
// `UnionExec` maintains input order
//
// It might be too strict here in the case that the input ordering are
compatible but not exactly the same.
// For example one input ordering has the ordering spec
SortExpr('a','b','c') and the other has the ordering
// spec SortExpr('a'), It is safe to derive the out ordering with the
spec SortExpr('a').
!self.partition_aware
&& first_input_ordering.is_some()
&& self
.inputs
.iter()
.map(|plan| plan.output_ordering())
.all(|ordering| {
ordering.is_some()
&& sort_expr_list_eq_strict_order(
ordering.unwrap(),
first_input_ordering.unwrap(),
)
})
}
```
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