Before release 8.1., Vertica users could denormalize their data by combining all fact and dimension table columns in a single ‘fat’ table. These tables facilitated faster query execution. However, this approach required users to maintain redundant sets of normalized and denormalized data, which incurred its own overhead.
Vertica 8.1 addressed this issue by introducing flattened tables. Flattened tables include columns that get their values by querying other tables. Operations on the source tables and flattened table are decoupled: changes in one are not automatically propagated to the other. Instead, columns are populated with queried data only when the column is created, or when you explicitly refresh it. This approach minimizes the overhead that is otherwise typical of conventional denormalized tables.
Read more about "Flattened Tables" here: