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Connect to PostgreSQL as an External Data Source using PolyBase

Use the CData ODBC Driver for PostgreSQL and PolyBase to create an external data source in SQL Server 2019 with access to live PostgreSQL data.

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

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

Connect to PostgreSQL

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 PostgreSQL Sys is created automatically).

To connect to PostgreSQL, set the Server, Port (the default port is 5432), and Database connection properties and set the User and Password you wish to use to authenticate to the server. If the Database property is not specified, the data provider connects to the user's default database.

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

Create an External Data Source for PostgreSQL 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 PostgreSQL data.

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

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

Create an External Data Source for PostgreSQL

Execute the following SQL command to create an external data source for PostgreSQL with PolyBase, using the DSN and credentials configured earlier.

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

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

Create External Tables for PostgreSQL

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

CREATE EXTERNAL TABLE Orders(
  ShipName [nvarchar](255) NULL,
  ShipCity [nvarchar](255) NULL,
  ...
) WITH ( 
  LOCATION='Orders',
  DATA_SOURCE=cdata_postgresql_source
);

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