jonahgao commented on code in PR #14102:
URL: https://github.com/apache/datafusion/pull/14102#discussion_r1912755777
##########
datafusion/expr/src/utils.rs:
##########
@@ -379,14 +379,12 @@ fn get_exprs_except_skipped(
}
}
-/// Resolves an `Expr::Wildcard` to a collection of `Expr::Column`'s.
-pub fn expand_wildcard(
- schema: &DFSchema,
- plan: &LogicalPlan,
- wildcard_options: Option<&WildcardOptions>,
-) -> Result<Vec<Expr>> {
+/// For each column specified in the USING JOIN condition, the JOIN plan
outputs it twice
+/// (once for each join side), but an unqualified wildcard should include it
only once.
+/// This function returns the columns that should be excluded.
+fn exclude_using_columns(plan: &LogicalPlan) -> Result<HashSet<Column>> {
let using_columns = plan.using_columns()?;
Review Comment:
[using_columns()](https://github.com/apache/datafusion/blob/f9cc3325cdb5891b7566a6f3503c1f7ac6ad51e0/datafusion/expr/src/logical_plan/plan.rs#L485)
finds join condition columns by traversing the plan tree. This manner might be
unsafe as it could incorrectly find columns that are not relevant to the
current SQL context. For example, the result of the query below is different
from other databases.
```sql
create table t(a int);
insert into t values(1),(2),(3);
select * from (select t.a+2 as a from t join t t2 using(a)) as t2;
```
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