Delegation Rules: SELECT Clause - Latest

The SELECT clause is the second phrase of an SQL query to be evaluated, following the WHERE clause since the SELECT clause acts on the subset of rows determined by the WHERE clause. If the data source provider supports the operations in the SELECT it is considered for delegation. 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 non-boolean operators in the SELECT clause can be delegated if the data source provider supports them.
6. Functions and non-boolean operators in a non-aggregating query cannot be delegated to a data provider.