LiaCastaneda commented on code in PR #16454:
URL: https://github.com/apache/datafusion/pull/16454#discussion_r2158853002
##########
datafusion/core/src/physical_planner.rs:
##########
@@ -969,8 +972,24 @@ impl DefaultPhysicalPlanner {
// Remove temporary projected columns
if left_projected || right_projected {
- let final_join_result =
-
join_schema.iter().map(Expr::from).collect::<Vec<_>>();
+ // Re-qualify the join schema only if the inputs were
previously requalified in
+ // `try_new_with_project_input`. This ensures that
when building the Projection
+ // it can correctly resolve field nullability and data
types
+ // by disambiguating fields from the left and right
sides of the join.
+ let qualified_join_schema = if requalified {
+ Arc::new(qualify_join_schema_sides(
+ join_schema,
+ original_left,
+ original_right,
+ )?)
+ } else {
+ Arc::clone(join_schema)
+ };
Review Comment:
The rationale for qualifying the schema is that when building the logical
`Projection` after, it will build the fields out of the expression names in
[exprlist_to_fields](https://github.com/apache/datafusion/blob/d8ee8d894abf4f60a4799a0129be07c6e1f38473/datafusion/expr/src/logical_plan/plan.rs#L2189)
so it will look in `new_join.schema()` and try to match each expr to a field
in the schema, if the expr::Column does not have a qualifier and there are
multiple candidates `Fields` that could correspond to this expr::Column , we
will get an
[ambiguity](https://github.com/apache/datafusion/blob/d8ee8d894abf4f60a4799a0129be07c6e1f38473/datafusion/common/src/dfschema.rs#L484)
error, qualifying the schema allows us to prevent this.
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