PolyBase external tables

External tables provide SQL Server with the schema to reason over data in the external data source. When you create an external table, you are establishing a strongly typed interface to the data that includes data type, nullability, and column-level collation. The columns can, and should, be strongly typed as this improves query performance and data quality.

Note

The data that you reference via an external table is not directly under SQL Server management. This means that the data could change or be removed and will not be included in operations such as backup or restore.

The columns in an external table are mapped by position and so you can choose whatever column names you like. You can, therefore, treat external tables as a useful abstraction for aliasing column names. In this sense, an external table operates as a view:

CREATE EXTERNAL TABLE [Sales].[SalesTerritory]
([TerritoryID]       INT    ...