How to connect PolyBase to Snowflake

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

Connect to Snowflake

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 Snowflake Sys is created automatically).

To connect to Snowflake:

1. Set User and Password to your Snowflake credentials and set the AuthScheme property to PASSWORD or OKTA.
2. Set URL to the URL of the Snowflake instance (i.e.: https://myaccount.snowflakecomputing.com).
3. Set Warehouse to the Snowflake warehouse.
4. (Optional) Set Account to your Snowflake account if your URL does not conform to the format above.
5. (Optional) Set Database and Schema to restrict the tables and views exposed.

See the Getting Started guide in the CData driver documentation for more information.

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

Create an External Data Source for Snowflake 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 Snowflake data.

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

CREATE DATABASE SCOPED CREDENTIAL snowflake_creds
WITH IDENTITY = 'snowflake_username', SECRET = 'snowflake_password';

Create an External Data Source for Snowflake

Execute a CREATE EXTERNAL DATA SOURCE SQL command to create an external data source for Snowflake 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_snowflake_source
WITH ( 
  LOCATION = 'odbc://SERVER_URL',
  CONNECTION_OPTIONS = 'DSN=CData Snowflake Sys',
  -- PUSHDOWN = ON | OFF,
  CREDENTIAL = snowflake_creds
);

Create External Tables for Snowflake

After creating the external data source, use CREATE EXTERNAL TABLE statements to link to Snowflake data from your SQL Server instance. The table column definitions must match those exposed by the CData ODBC Driver for Snowflake. 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 Snowflake 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_snowflake_source
);

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