adriangb commented on code in PR #25412:
URL: https://github.com/apache/datafusion/pull/25412#discussion_r4038668131
##########
datafusion/optimizer/src/extract_leaf_expressions.rs:
##########
@@ -702,27 +720,36 @@ fn build_extraction_projection_impl(
// than target_schema (the projection's output) because columns
produced
// by alias expressions (e.g., CSE's __common_expr_N) exist in the
output but
// not the input, and cannot be added as pass-through Column
references.
+ //
+ // Both sides of that check are read in the input's own spelling. A
column can
+ // arrive here unqualified while the input names it `t.c`, and the
other way round:
+ // a projection of bare names over a qualified input is what
eliminating one side
+ // of a union leaves behind. Resolving both sides lets a pass-through
the
+ // projection already carries match the one about to be added, and
pushes the one
+ // that is genuinely new under the name the input gives it. Left
unresolved, the
+ // merged projection would hold `t.c` and a bare `c` together, which
+ // `Projection::try_new` rejects as ambiguous.
+ let input_schema = existing.input.schema();
let existing_cols: IndexSet<Column> = existing
.expr
.iter()
.filter_map(|e| {
if let Expr::Column(c) = e {
- Some(c.clone())
+ resolve_against(input_schema, c)
Review Comment:
Fixed in 5e7ec7a266: the existing side now collects `passthrough_column(e)`,
so `t.c AS c` counts the same as a bare `t.c`. Added
`test_merge_into_projection_with_same_name_alias`, which fails without the
change with `AmbiguousReference { test.a }`. A same-name alias case in SQL does
not reach this path (the planner drops `env AS env` first), so the regression
test is a unit test.
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