How to connect PolyBase to CSV

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

Connect to CSV

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 CSV Sys is created automatically).

The DataSource property must be set to a valid local folder name.

Also, specify the IncludeFiles property to work with text files having extensions that differ from .csv, .tab, or .txt. Specify multiple file extensions in a comma-separated list. You can also set Extended Properties compatible with the Microsoft Jet OLE DB 4.0 driver. Alternatively, you can provide the format of text files in a Schema.ini file.

Set UseRowNumbers to true if you are deleting or updating in CSV. This will create a new column with the name RowNumber which will be used as key for that table.

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

Create an External Data Source for CSV 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 CSV data.

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

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

Create an External Data Source for CSV

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

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

For CSV, 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_csv_source
WITH ( 
  LOCATION = 'odbc://SERVER_URL',
  CONNECTION_OPTIONS = 'DSN=CData CSV Sys',
  -- PUSHDOWN = ON | OFF,
  CREDENTIAL = csv_creds
);

Create External Tables for CSV

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

CREATE EXTERNAL TABLE Customer(
  City [nvarchar](255) NULL,
  TotalDue [nvarchar](255) NULL,
  ...
) WITH ( 
  LOCATION='Customer',
  DATA_SOURCE=cdata_csv_source
);

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