Configure PolyBase to access external data in SQL Server
This article explains how to use PolyBase on a SQL Server instance to query external data in another SQL Server instance.
Before creating a database scoped credential a Master Key must be created.
Configure a SQL Server external data source
To query the data from a SQL Server data source, you must create external tables to reference the external data. This section provides sample code to create these external tables.
For optimal query performance, create statistics on external table columns, especially for the ones used for joins, filters, and aggregates.
The following Transact-SQL commands are used in this section:
- CREATE DATABASE SCOPED CREDENTIAL (Transact-SQL)
- CREATE EXTERNAL DATA SOURCE (Transact-SQL)
- CREATE STATISTICS (Transact-SQL)
Create a database scoped credential for accessing the MongoDB source.
/* specify credentials to external data source * IDENTITY: user name for external source. * SECRET: password for external source. */ CREATE DATABASE SCOPED CREDENTIAL SqlServerCredentials WITH IDENTITY = 'username', Secret = 'password';
Create an external data source with CREATE EXTERNAL DATA SOURCE.
/* LOCATION: Location string should be of format '<vendor>://<server>[:<port>]'. * PUSHDOWN: specify whether computation should be pushed down to the source. ON by default. * CREDENTIAL: the database scoped credential, created above. */ CREATE EXTERNAL DATA SOURCE SQLServerInstance WITH ( LOCATION = 'sqlserver://SqlServer', -- PUSHDOWN = ON | OFF, CREDENTIAL = SQLServerCredentials);
Optional: Create statistics on an external table.
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We recommend creating statistics on external table columns, especially the ones used for joins, filters and aggregates, for optimal query performance. ```sql CREATE STATISTICS statistics_name ON customer (C_CUSTKEY) WITH FULLSCAN; ```
Once you have created an external data source, you can use the CREATE EXTERNAL TABLE command to create a queryable table over that source.
SQL Server connector compatible types
You can make a connection to other data sources that recognizes a SQL Server connection. Use the SQL Server PolyBase connector to create an external table of both Azure SQL Data Warehouse and Azure SQL Database. To accomplish this task, follow the same steps listed previously. Make sure the database scoped credential, server address, port, and location string correlate to that of the compatible data source you want to connect to.
To learn more about PolyBase, see Overview of SQL Server PolyBase.