adriangb commented on code in PR #20117:
URL: https://github.com/apache/datafusion/pull/20117#discussion_r2801311700
##########
datafusion/optimizer/src/optimize_projections/mod.rs:
##########
@@ -559,7 +559,19 @@ fn merge_consecutive_projections(proj: Projection) ->
Result<Transformed<Project
metadata,
}) => rewrite_expr(*expr, &prev_projection).map(|result| {
result.update_data(|expr| {
- Expr::Alias(Alias::new(expr, relation,
name).with_metadata(metadata))
+ // After substitution, the inner expression may now have
the
+ // same schema_name as the alias (e.g. when an extraction
+ // alias like `__extracted_1 AS f(x)` is resolved back to
+ // `f(x)`). Wrapping in a redundant self-alias causes a
+ // cosmetic `f(x) AS f(x)` due to Display vs schema_name
+ // formatting differences. Drop the alias when it matches.
+ if expr.schema_name().to_string() == name {
Review Comment:
Generally we try to preserve metadata where "sensible". We probably don't do
it well everywhere we should.
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