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Introducing Microsoft SQL Server 2019

You're reading from   Introducing Microsoft SQL Server 2019 Reliability, scalability, and security both on premises and in the cloud

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Product type Paperback
Published in Apr 2020
Publisher Packt
ISBN-13 9781838826215
Length 488 pages
Edition 1st Edition
Languages
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Authors (8):
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Allan Hirt Allan Hirt
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Allan Hirt
Dustin Ryan Dustin Ryan
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Dustin Ryan
Mitchell Pearson Mitchell Pearson
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Mitchell Pearson
Kellyn Gorman Kellyn Gorman
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Kellyn Gorman
Dave Noderer Dave Noderer
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Dave Noderer
Buck Woody Buck Woody
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Buck Woody
Arun Sirpal Arun Sirpal
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Arun Sirpal
James Rowland-Jones James Rowland-Jones
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James Rowland-Jones
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Toc

Table of Contents (15) Chapters Close

Preface 1. Optimizing for performance, scalability and real‑time insights 2. Enterprise Security FREE CHAPTER 3. High Availability and Disaster Recovery 4. Hybrid Features – SQL Server and Microsoft Azure 5. SQL Server 2019 on Linux 6. SQL Server 2019 in Containers and Kubernetes 7. Data Virtualization 8. Machine Learning Services Extensibility Framework 9. SQL Server 2019 Big Data Clusters 10. Enhancing the Developer Experience 11. Data Warehousing 12. Analysis Services 13. Power BI Report Server 14. Modernization to the Azure Cloud

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    ...
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