sgrebnov commented on code in PR #12482:
URL: https://github.com/apache/datafusion/pull/12482#discussion_r1761390609
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datafusion/sql/src/unparser/rewrite.rs:
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@@ -258,8 +258,36 @@ pub(super) fn subquery_alias_inner_query_and_columns(
(outer_projections.input.as_ref(), columns)
}
-/// Injects column aliases into the projection of a logical plan by wrapping
`Expr::Column` expressions
-/// with `Expr::Alias` using the provided list of aliases. Non-column
expressions are left unchanged.
+/// Injects column aliases into a subquery's logical plan. The function
searches for a `Projection`
+/// within the given plan, which may be wrapped by other operators (e.g.,
LIMIT, SORT).
+/// If the top-level plan is a `Projection`, it directly injects the column
aliases.
+/// Otherwise, it iterates through the plan's children to locate and transform
the `Projection`.
+///
+/// Example:
+/// - `SELECT col1, col2 FROM table LIMIT 10` plan with aliases `["alias_1",
"some_alias_2"]` will be transformed to
+/// - `SELECT col1 AS alias_1, col2 AS some_alias_2 FROM table LIMIT 10`
+pub(super) fn inject_column_aliases_into_subquery(
+ plan: LogicalPlan,
+ aliases: Vec<Ident>,
+) -> Result<LogicalPlan> {
+ match &plan {
+ LogicalPlan::Projection(inner_p) => Ok(inject_column_aliases(inner_p,
aliases)),
+ _ => {
+ // projection is wrapped by other operator (LIMIT, SORT, etc),
iterate through the plan to find it
+ plan.map_children(|child| {
+ if let LogicalPlan::Projection(p) = &child {
+ Ok(Transformed::yes(inject_column_aliases(p,
aliases.clone())))
Review Comment:
@dmitrybugakov - good point, the aliases will actually be cloned only once
for the subquery projection, which can only be singular. I also reviewed
whether it makes sense to borrow aliases and clone them in
`inject_column_aliases`, but allowing the function to consume the provided
aliases seems the right approach so it can be used without extra aliases
cloning inside.
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