Adding Join Constraints That Facilitate Joining to Other Tables
Include join constraint columns that support joining to tables not defined in the join index. It makes no difference whether you assign these columns to the fixed part of the join index or to the repeating part.
For example, you might carry the join columns c_nationkey and l_partkey in the join index to facilitate joining the nation and parts tables to the join index.
When the join index is defined using an outer join, use the outer table join column rather than the inner table join column to enhance performance.