peter-toth commented on code in PR #10832:
URL: https://github.com/apache/datafusion/pull/10832#discussion_r1632037636
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datafusion/optimizer/src/common_subexpr_eliminate.rs:
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@@ -782,9 +786,11 @@ impl TreeNodeRewriter for CommonSubexprRewriter<'_> {
return Ok(Transformed::new(expr, false, TreeNodeRecursion::Jump));
}
- let (up_index, expr_id) = &self.id_array[self.down_index];
+ let (up_index, expr_id, aliased) = &self.id_array[self.down_index];
self.down_index += 1;
+ self.aliased |= aliased;
Review Comment:
This looks suspicuous to me. We don't need to alias if any of the ancestor
nodes is an alias, do we? But the `f_down()` is called DFS way so if we
calculate `self.aliased` as `self.aliased |= aliased` then we can take into
account other nodes than just the ancestors in 2nd+ childrens.
I think we need to maintain some kind of boolan stack with
`f_down()`/`f_up()` of `CommonSubexprRewriter` to decide about aliasing.
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