How to connect PolyBase to MongoDB

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

Connect to MongoDB

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 MongoDB Sys is created automatically).

Set the Server, Database, User, and Password connection properties to connect to MongoDB. To access MongoDB collections as tables you can use automatic schema discovery or write your own schema definitions. Schemas are defined in .rsd files, which have a simple format. You can also execute free-form queries that are not tied to the schema.

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

Create an External Data Source for MongoDB 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 MongoDB data.

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

CREATE DATABASE SCOPED CREDENTIAL mongodb_creds
WITH IDENTITY = 'mongodb_username', SECRET = 'mongodb_password';

Create an External Data Source for MongoDB

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

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

NOTE: SERVERNAME and PORT corresponds to the Server and Port connection properties for MongoDB. PUSHDOWN is set to ON by default, meaning the ODBC Driver can leverage server-side processing for complex queries.

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

Create External Tables for MongoDB

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

CREATE EXTERNAL TABLE restaurants(
  borough [nvarchar](255) NULL,
  cuisine [nvarchar](255) NULL,
  ...
) WITH ( 
  LOCATION='restaurants',
  DATA_SOURCE=cdata_mongodb_source
);

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