How to connect PolyBase to Cosmos DB

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 Cosmos DB, you get access to your Cosmos DB data directly alongside your SQL Server data. This article describes creating an external data source and external tables to grant access to live Cosmos DB 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 Cosmos DB data using PolyBase due to optimized data processing built into the driver. When you issue complex SQL queries from SQL Server to Cosmos DB, the driver pushes down supported SQL operations, like filters and aggregations, directly to Cosmos DB 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 Cosmos DB data, using a single query to pull data from distributed sources.

Connect to Cosmos DB

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 Cosmos DB Sys is created automatically).

To obtain the connection string needed to connect to a Cosmos DB account using the SQL API, log in to the Azure Portal, select Azure Cosmos DB, and select your account. In the Settings section, click Connection String and set the following values:

• AccountEndpoint: The Cosmos DB account URL from the Keys blade of the Cosmos DB account
• AccountKey: In the Azure portal, navigate to the Cosmos DB service and select your Azure Cosmos DB account. From the resource menu, go to the Keys page. Find the PRIMARY KEY value and set AccountKey to this value.

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

Create an External Data Source for Cosmos DB 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 Cosmos DB data.

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

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

Create an External Data Source for Cosmos DB

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

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

For Cosmos DB, set SERVERNAME to the URL or address for your server (e.g. 'localhost' or '127.0.0.1' for local servers; the remote URL for remote servers). 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_cosmosdb_source
WITH ( 
  LOCATION = 'odbc://SERVER_URL',
  CONNECTION_OPTIONS = 'DSN=CData Cosmos DB Sys',
  -- PUSHDOWN = ON | OFF,
  CREDENTIAL = cosmosdb_creds
);

Create External Tables for Cosmos DB

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

CREATE EXTERNAL TABLE Customers(
  City [nvarchar](255) NULL,
  CompanyName [nvarchar](255) NULL,
  ...
) WITH ( 
  LOCATION='Customers',
  DATA_SOURCE=cdata_cosmosdb_source
);

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