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10.5. Multi-Source Models: Planning and Execution
The planner logically treats a multi-source table as if it were a view containing the union all of the respective source tables. More complex partitioning scenarios, such as heterogeneous sources or list partitioning will require the use of a Partitioned Union.
Most of the federated optimizations available over unions are still applicable in multi-source mode. This includes aggregation pushdown/decomposition, limit pushdown, join partitioning, etc.
