How to connect PolyBase to Stack Exchange

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 API Driver for ODBC, you get access to your Stack Exchange data directly alongside your SQL Server data. This article describes creating an external data source and external tables to grant access to live Stack Exchange data using T-SQL queries.

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

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

Connect to Stack Exchange

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 Stack Exchange Sys is created automatically).

Start by setting the Profile connection property to the location of the Stack Exchange Profile on disk (e.g. C:\profiles\StackExchange.apip). Next, set the ProfileSettings connection property to the connection string for Stack Exchange (see below).

Stack Exchange API Profile Settings

Register an application on StackApps to obtain an API Key. The Site property specifies which Stack Exchange site to query (e.g., stackoverflow).

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

Create an External Data Source for Stack Exchange 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 Stack Exchange data.

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

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

Create an External Data Source for Stack Exchange

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

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

For Stack Exchange, 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_api_source
WITH ( 
  LOCATION = 'odbc://SERVER_URL',
  CONNECTION_OPTIONS = 'DSN=CData Stack Exchange Sys',
  -- PUSHDOWN = ON | OFF,
  CREDENTIAL = api_creds
);

Create External Tables for Stack Exchange

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

CREATE EXTERNAL TABLE Answers(
  AnswerId [nvarchar](255) NULL,
  CreationDate [nvarchar](255) NULL,
  ...
) WITH ( 
  LOCATION='Answers',
  DATA_SOURCE=cdata_api_source
);

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