Delegation Rules: SELECT Clause for Aggregating Queries

The following rules apply when determining what can be delegated to a data provider:

1. All data source providers must support returning all columns from a data source.
2. All data source providers must support returning a subset of the columns in the data source.
3. All data source providers must support aliasing of an attribute in the SELECT clause.
4. All data source providers must be able to return an attribute from the data source in any order.
5. Aggregating functions and operators must be in the SELECT clause.