How to connect PolyBase to Azure Synapse

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 Synapse, you get access to your Azure Synapse data directly alongside your SQL Server data. This article describes creating an external data source and external tables to grant access to live Azure Synapse data using T-SQL queries.

NOTE: PolyBase is only available on SQL Server 19 and above, and only for Standard SQL Server.

The CData ODBC drivers offer unmatched performance for interacting with live Azure Synapse data using PolyBase due to optimized data processing built into the driver. When you issue complex SQL queries from SQL Server to Azure Synapse, the driver pushes down supported SQL operations, like filters and aggregations, directly to Azure Synapse 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 Synapse data, using a single query to pull data from distributed sources.

Connect to Azure Synapse

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 Synapse Sys is created automatically).

Connecting to Azure Synapse

In addition to providing authentication (see below), set the following properties to connect to a Azure Synapse database:

• Server: The server running Azure. You can find this by logging into the Azure portal and navigating to Azure Synapse Analytics -> Select your database -> Overview -> Server name.
• Database: The name of the database, as seen in the Azure portal on the Azure Synapse Analytics page.

Authenticating to Azure Synapse

Connect to Azure Synapse using the following properties:

• User: The username provided for authentication with Azure.
• Password: The password associated with the authenticating user.

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

Create an External Data Source for Azure Synapse 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 Synapse data.

NOTE: IDENTITY and SECRET correspond with the User and Password properties for Azure Synapse.

CREATE DATABASE SCOPED CREDENTIAL azuresynapse_creds
WITH IDENTITY = 'azuresynapse_username', SECRET = 'azuresynapse_password';

Create an External Data Source for Azure Synapse

Execute a CREATE EXTERNAL DATA SOURCE SQL command to create an external data source for Azure Synapse with PolyBase:

• Set the LOCATION parameter , using the DSN and credentials configured earlier.

PUSHDOWN is set to ON by default, meaning the ODBC Driver can leverage server-side processing for complex queries.

CREATE EXTERNAL DATA SOURCE cdata_azuresynapse_source
WITH ( 
  LOCATION = 'odbc://SERVER_URL',
  CONNECTION_OPTIONS = 'DSN=CData Azure Synapse Sys',
  -- PUSHDOWN = ON | OFF,
  CREDENTIAL = azuresynapse_creds
);

Create External Tables for Azure Synapse

After creating the external data source, use CREATE EXTERNAL TABLE statements to link to Azure Synapse data from your SQL Server instance. The table column definitions must match those exposed by the CData ODBC Driver for Azure Synapse. 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 Synapse Products would look similar to the following:

CREATE EXTERNAL TABLE Products(
  Id [nvarchar](255) NULL,
  ProductName [nvarchar](255) NULL,
  ...
) WITH ( 
  LOCATION='Products',
  DATA_SOURCE=cdata_azuresynapse_source
);

Having created external tables for Azure Synapse 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 Synapse, freeing up local resources and computing power. Download a free, 30-day trial of the ODBC Driver for Azure Synapse and start working with live Azure Synapse data alongside your SQL Server data today.