Projections and aggregates

In a current Postgres project, I have summary tables that are populated with a key of fewer columns than the source table, and all of the fact columns SUMmed. In this case, the summary tables are grouped and clustered in a different order from the source. For example, if the source has a key of (col1, col2, col3), the summary table is grouped by col1, col3.

Since aggregates can't be part of a projection, would the performant approach in Vertica 7 be to create a projection with the summary key order, then create a view on top of that with the column SUMs? Or is the projection unnecessary?

Example:

CREATE TABLE source (key1, key2, key3, fact1);
CREATE PROJECTION summary_projection AS SELECT key1, key3, fact1 FROM source ORDER BY key1, key3;
CREATE VIEW summary_view AS SELECT key1, key3, SUM(fact1)  GROUP BY key1, key3;