Loopback connection to SQL Server from a Python or R script

APPLIES TO: yesSQL Server noAzure SQL Database noAzure Synapse Analytics (SQL DW) noParallel Data Warehouse

Learn how to use a loopback connection to connect back to SQL Server over ODBC to read or write data from a Python or R script executed from sp_execute_external_script. You can use this when using the InputDataSet and OutputDataSet arguments of sp_execute_external_script are not possible.

Connection string

To make a loopback connection, you need to use a correct connection string. The common mandatory arguments are the name of the ODBC driver, the server address, and the name of database.

Connection string on Windows

For authentication on SQL Server on Windows, the Python or R script can use the Trusted_Connection connection string attribute to authenticate as the same user that ran the sp_execute_external_script.

Here is an example of the loopback connection string on Windows:

"Driver=SQL Server;Server=.;Database=nameOfDatabase;Trusted_Connection=Yes;"

Connection string on Linux

For authentication on SQL Server on Linux, the Python or R script needs to use ClientCertificate and ClientKey attributes of the ODBC driver to authenticate as the same user that executed sp_execute_external_script. This requires the use of latest ODBC driver version 17.4.1.1.

Here is an example of the loopback connection string on Linux:

"Driver=ODBC Driver 17 for SQL Server;Server=fe80::8012:3df5:0:5db1%eth0;Database=nameOfDatabase;ClientCertificate=file:/var/opt/mssql-extensibility/data/baeaac72-60b3-4fae-acfd-c50eff5d34a2/sqlsatellitecert.pem;ClientKey=file:/var/opt/mssql-extensibility/data/baeaac72-60b3-4fae-acfd-c50eff5d34a2/sqlsatellitekey.pem;TrustServerCertificate=Yes;Trusted_Connection=no;Encrypt=Yes"

The server address, client certificate file location, and client key file location are unique to every sp_execute_external_script and can be obtained by the use of the API rx_get_sql_loopback_connection_string() for Python or rxGetSqlLoopbackConnectionString() for R.

For more information on the connection string attributes, see the DSN and Connection String Keywords and Attributes for Microsoft ODBC Driver for SQL Server.

Generate connection string with revoscalepy for Python

You can use the API rx_get_sql_loopback_connection_string() in revoscalepy to generate a correct connection string for a loopback connection in a Python script.

It accepts the following arguments:

Argument Description
name_of_database Name of the database to which the connection is to be made
odbc_driver Name of the odbc driver

Examples

Example for SQL Server on Windows:

EXECUTE sp_execute_external_script
@language = N'Python',
@script = N'
from revoscalepy import rx_get_sql_loopback_connection_string, RxSqlServerData, rx_data_step
loopback_connection_string = rx_get_sql_loopback_connection_string(odbc_driver="SQL Server", name_of_database="DBName")
print("Connection String:{0}".format(loopback_connection_string))
data_set = RxSqlServerData(sql_query = "select col1, col2 from tableName",
                           connection_string = loopback_connection_string)
OutputDataSet = rx_data_step(data_set)
'
WITH RESULT SETS ((col1 int, col2 int))
GO

Example for SQL Server on Linux:

EXECUTE sp_execute_external_script
@language = N'Python',
@script = N'
from revoscalepy import rx_get_sql_loopback_connection_string, RxSqlServerData, rx_data_step
loopback_connection_string = rx_get_sql_loopback_connection_string(odbc_driver="ODBC Driver 17 for SQL Server",
                                                                   name_of_database="DBName")
print("Loopback Connection String:{0}".format(loopback_connection_string))
data_set = RxSqlServerData(sql_query = "select col1, col2 from tableName",
                           connection_string = loopback_connection_string)
OutputDataSet = rx_data_step(data_set)
'
WITH RESULT SETS ((col1 int, col2 int))
GO

Generate connection string with RevoScaleR for R

You can use the API rxGetSqlLoopbackConnectionString() in RevoScaleR to generate a correct connection string for a loopback connection in an R script.

It accepts the following arguments:

Argument Description
nameOfDatabase Name of the database to which the connection is to be made
odbcDriver Name of the odbc driver

Examples

Example for SQL Server on Windows:

EXECUTE sp_execute_external_script
@language = N'R',
@script = N'
    loopbackConnectionString <- rxGetSqlLoopbackConnectionString(nameOfDatabase="DBName", odbcDriver ="SQL Server")
    print(paste("Connection String:", loopbackConnectionString))
    dataSet <- RxSqlServerData(sqlQuery = "select col1, col2 from tableName",
                               connectionString = loopbackConnectionString)
    OutputDataSet <- rxDataStep(dataSet)
'
WITH RESULT SETS ((col1 int, col2 int))
GO

Example for SQL Server on Linux:

EXECUTE sp_execute_external_script
@language = N'R',
@script = N'
    loopbackConnectionString <-  rxGetSqlLoopbackConnectionString(nameOfDatabase="DBName", 
                                                                  odbcDriver ="ODBC Driver 17 for SQL Server")
    print(paste("Connection String:", loopbackConnectionString))
    dataSet <- RxSqlServerData(sqlQuery = "select col1, col2 from tableName", 
                               connectionString = loopbackConnectionString)
    OutputDataSet <- rxDataStep(dataSet)
'
WITH RESULT SETS ((col1 int, col2 int))
GO

Next steps