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Connect to Azure Table as an External Data Source using PolyBase

Use the CData ODBC Driver for Azure Table and PolyBase to create an external data source in SQL Server 2019 with access to live Azure Table data.

PolyBase for SQL Server allows you to query external data by using the same Transact-SQL syntax used to query a database table. When paired with the CData ODBC Driver for Azure Table, you get access to your Azure Table data directly alongside your SQL Server data. This article walks through creating an external data source and external tables to grant access to live Azure Table data using T-SQL queries.

The CData ODBC drivers offer unmatched performance for interacting with live Azure Table data using PolyBase due to optimized data processing built into the driver. When you issue complex SQL queries from SQL Server to Azure Table, the driver pushes down supported SQL operations, like filters and aggregations, directly to Azure Table and utilizes the embedded SQL engine to process unsupported operations (often SQL functions and JOIN operations) client-side. And with PolyBase, you can also join SQL Server data with Azure Table data, using a single query to pull data from distributed sources.

Connect to Azure Table

If you have not already, first specify connection properties in an ODBC DSN (data source name). This is the last step of the driver installation. You can use the Microsoft ODBC Data Source Administrator to create and configure ODBC DSNs. To create an external data source in SQL Server using PolyBase, configure a System DSN (CData Azure Table Sys is created automatically).

Specify your AccessKey and your Account to connect. Set the Account property to the Storage Account Name and set AccessKey to one of the Access Keys. Either the Primary or Secondary Access Keys can be used. To obtain these values, navigate to the Storage Accounts blade in the Azure portal. You can obtain the access key by selecting your account and clicking Access Keys in the Settings section.

Click "Test Connection" to ensure that the DSN is connected to Azure Table properly. Navigate to the Tables tab to review the table definitions for Azure Table.

Create an External Data Source for Azure Table Data

After configuring the connection, you need to create a master encryption key and a credential database for the external data source.

Creating a Master Encryption Key

Execute the following SQL command to create a new master key, 'ENCRYPTION,' to encrypt the credentials for the external data source.

CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'password';

Creating a Credential Database

Execute the following SQL command to create credentials for the external data source connected to Azure Table data.

NOTE: Since Azure Table does not require a User or Password to authenticate, you may use whatever values you wish for IDENTITY and SECRET.

CREATE DATABASE SCOPED CREDENTIAL azuretables_creds
WITH IDENTITY = 'username', SECRET = 'password';

Create an External Data Source for Azure Table

Execute the following SQL command to create an external data source for Azure Table with PolyBase, using the DSN and credentials configured earlier.

For Azure Table, set SERVERNAME to 'localhost' or '127.0.0.1' and leave PORT empty. PUSHDOWN is set to ON by default, meaning the ODBC Driver can leverage server-side processing for complex queries.

CREATE EXTERNAL DATA SOURCE cdata_azuretables_source
WITH ( 
  LOCATION = 'odbc://SERVERNAME[:PORT]',
  CONNECTION_OPTIONS = 'DSN=CData Azure Table Sys',
  -- PUSHDOWN = ON | OFF,
  CREDENTIAL = azuretables_creds
);

Create External Tables for Azure Table

After creating the external data source, use CREATE EXTERNAL TABLE statements to link to Azure Table data from your SQL Server instance. The table column definitions must match those exposed by the CData ODBC Driver for Azure Table. You can refer to the Tables tab of the DSN Configuration Wizard to see the table definition.

Sample CREATE TABLE Statement

The statement to create an external table based on a Azure Table NorthwindProducts would look similar to the following:

CREATE EXTERNAL TABLE NorthwindProducts(
  Name [nvarchar](255) NULL,
  Price [nvarchar](255) NULL,
  ...
) WITH ( 
  LOCATION='NorthwindProducts',
  DATA_SOURCE=cdata_azuretables_source
);

Having created external tables for Azure Table in your SQL Server instance, you are now able to query local and remote data simultaneously. Thanks to built-in query processing in the CData ODBC Driver, you know that as much query processing as possible is being pushed to Azure Table, freeing up local resources and computing power. Download a free, 30-day trial of the ODBC Driver for Azure Table and start working with live Azure Table data alongside your SQL Server data today.