Declarative partitioning was a long-awaited feature and has been enhanced since its introduction in PostgreSQL 10. However, for many users, finding optimal partitioning schemes to have the best benefits from partitioning is not an easy task. Therefore, we added in HypoPG a new hypothetical partitioning feature which helps users to design partitioning. In this presentation, I will provide a brief introduction of HypoPG and explain declarative partitioning, and then I'll show the usage of hypothetical partitioning feature and explain how the extension is working.