Function reorder_output_after_swap 

pub fn reorder_output_after_swap(
    plan: Arc<dyn ExecutionPlan>,
    left_schema: &Schema,
    right_schema: &Schema,
) -> Result<Arc<dyn ExecutionPlan>>

When the order of the join inputs are changed, the output order of columns must remain the same.

Joins output columns from their left input followed by their right input. Thus if the inputs are reordered, the output columns must be reordered to match the original order.