Function qualify_join_schema_sides

datafusion/core/src/physical_planner.rs:2113–2161

Qualifies the fields in a join schema with "left" and "right" qualifiers without mutating the original schema. This function should only be used when the join inputs have already been requalified earlier in `try_new_with_project_input`. The purpose is to avoid ambiguity errors later in planning (e.g., in nullability or data type resolution) when converting expressions to fields.

(
    join_schema: &DFSchema,
    left: &LogicalPlan,
    right: &LogicalPlan,
)

/// The purpose is to avoid ambiguity errors later in planning (e.g., in nullability or data type resolution)
/// when converting expressions to fields.
fn qualify_join_schema_sides(
    join_schema: &DFSchema,
    left: &LogicalPlan,
    right: &LogicalPlan,
) -> Result<DFSchema> {
    let left_fields = left.schema().fields();
    let right_fields = right.schema().fields();
    let join_fields = join_schema.fields();

    // Validate lengths
    assert_eq_or_internal_err!(
        join_fields.len(),
        left_fields.len() + right_fields.len(),
        "Join schema field count must match left and right field count."
    );

    // Validate field names match
    for (i, (field, expected)) in join_fields
        .iter()
        .zip(left_fields.iter().chain(right_fields.iter()))
        .enumerate()
    {
        assert_eq_or_internal_err!(
            field.name(),
            expected.name(),
            "Field name mismatch at index {}",
            i
        );
    }

    // qualify sides
    let qualifiers = join_fields
        .iter()
        .enumerate()
        .map(|(i, _)| {
            if i < left_fields.len() {
                Some(TableReference::Bare {
                    table: Arc::from("left"),
                })
            } else {
                Some(TableReference::Bare {
                    table: Arc::from("right"),
                })
            }
        })
        .collect();

    join_schema.with_field_specific_qualified_schema(qualifiers)
}

fn get_physical_expr_pair(
    expr: &Expr,