THIS TOPIC APPLIES TO: SQL Server (starting with 2016)Azure SQL DatabaseAzure SQL Data Warehouse Parallel Data Warehouse
Executes the script provided as argument at an external location. The script must be written in a supported and registered language. To execute sp_execute_external_script, you must first enable external scripts by using the statement,
sp_configure 'external scripts enabled', 1;.
sp_execute_external_script @language = N'language, @script = N'script' [ , @input_data_1 = N'input_data_1' ] [ , @input_data_1_name = N'input_data_1_name' ] [ , @output_data_1_name = N'output_data_1_name' ] [ , @parallel = 0 | 1 ] [ , @params = N'@parameter_name data_type [ OUT | OUTPUT ] [ ,...n ]' ] [ , @parameter1 = 'value1' [ OUT | OUTPUT ] [ ,...n ] ]
@language = N'language'
Indicates the script language. language is sysname.
Valid values are
@script = N'script'
External language script specified as a literal or variable input. script is nvarchar(max).
[ @input_data_1_name = N'input_data_1_name' ]
Specifies the name of the variable used to represent the query defined by @input_data_1. The data type of the variable in the external script depends on the language. In case of R, the input variable is a data frame. In the case of Python, input must be tabular. input_data_1_name is sysname.
Default value is
[ @input_data_1 = N'input_data_1' ]
Specifies the input data used by the external script in the form of a Transact-SQL query. The data type of input_data_1 is nvarchar(max).
[ @output_data_1_name = N'output_data_1_name' ]
Specifies the name of the variable in the external script that contains the data to be returned to SQL Server upon completion of the stored procedure call. The data type of the variable in the external script depends on the language. For R, the output must be a data frame. For Python, the output must be a pandas data frame. output_data_1_name is sysname.
Default value is "OutputDataSet".
[ @parallel = 0 | 1 ]
Enable parallel execution of R scripts by setting the
@parallel parameter to 1. The default for this parameter is 0 (no parallelism).
For R scripts that do not use RevoScaleR functions, using the
@parallel parameter can be beneficial for processing large datasets, assuming the script can be trivially parallelized. For example, when using the R
predict function with a model to generate new predictions, set
@parallel = 1 as a hint to the query engine. If the query can be parallelized, rows are distributed according to the MAXDOP setting.
@parallel = 1 and the output is being streamed directly to the client machine, then the
WITH RESULTS SETS clause is required and an output schema must be specified.
For R scripts that use RevoScaleR functions, parallel processing is handled automatically and you should not specify
@parallel = 1 to the sp_execute_external_script call.
[ @params = N'@parameter_name data_type [ OUT | OUTPUT ] [ ,...n ]' ]
A list of input parameter declarations that are used in the external script.
[ @parameter1 = 'value1' [ OUT | OUTPUT ] [ ,...n ] ]
A list of values for the input parameters used by the external script.
Use sp_execute_external_script to execute scripts written in a supported language. Currently, supported languages are R for SQL Server 2016, and Python and R for SQL Server 2017.
The query tree is controlled by SQL Server and users cannot perform arbitrary operations on the query.
By default, result sets returned by this stored procedure are output with unnamed columns. Column names used within a script are local to the scripting environment and are not reflected in the outputted result set. To name result set columns, use the
WITH RESULTS SET clause of
In addition to returning a result set, you can return scalar values to SQL Server by using OUTPUT parameters. The following example shows the use of the OUTPUT parameter to return the serialized R model that was used as input to the script:
In SQL Server, R Services (In-Database) is comprised of a server component installed with SQL Server, and a set of workstation tools and connectivity libraries that connect the data scientist to the high-performance environment of SQL Server. You must install the machine learning components during SQL Server setup to enable the execution of external scripts. For more information, see Set up SQL Server Machine Learning Services.
You can control the resources used by external scripts by configuring an external resource pool. For more information, see CREATE EXTERNAL RESOURCE POOL (Transact-SQL). Information about the workload can be obtained from the resource governor catalog views, DMV's, and counters. For more information, see Resource Governor Catalog Views (Transact-SQL), Resource Governor Related Dynamic Management Views (Transact-SQL), and SQL Server, External Scripts Object.
Streaming execution for R and Python scripts
Streaming allows the R or Python script to work with more data than can fit in memory. To control the number of rows passed during streaming, specify an integer value for the parameter,
@r_rowsPerRead in the
@params collection. For example, if you are training a model that uses very wide data, you could adjust the value to read fewer rows, to ensure that all rows can be sent in one chunk of data. You might also use this parameter to manage the number of rows being read and processed at one time, to mitigate server performance issues.
@r_rowsPerRead parameter for streaming and the
@parallel argument should be considered hints. For the hint to be applied, it must be possible to generate a SQL query plan that includes parallel processing. If this is not possible, parallel processing cannot be enabled.
Streaming and parallel processing are supported only in Enterprise Edition. You can include the parameters in your queries in Standard Edition without raising an error, but the parameters have no effect and R scripts run in a single process.
The following data types are not supported when used in the input query or parameters of
sp_execute_external_script procedure, and return an unsupported type error.
As a workaround, CAST the column or value to a supported type in Transact-SQL before sending it to the external script.
datetime2, datetimeoffset, time
hierarchyid, geometry, geography
CLR user-defined types
In general, any result set that cannot be mapped to a Transact-SQL data type, is output as NULL.
Restrictions specific to R
If the input includes datetime values that do not fit the permissible range of values in R, values are converted to NA. This is required because SQL Server permits a larger range of values than is supported in the R language.
Float values (for example,
NaN) are not supported in SQL Server even though both languages use IEEE 754. Current behavior just sends the values to SQL Server directly; as a result, the SQL client in Management Studio throws an error. Therefore, these values are converted to NULL.
Requires EXECUTE ANY EXTERNAL SCRIPT database permission.
This section contains examples of how this stored procedure can be used to execute R or Python scripts using Transact-SQL.
A. Return an R data set to SQL Server
The following example creates a stored procedure that uses sp_execute_external_script to return the Iris dataset included with R to SQL Server.
DROP PROC IF EXISTS get_iris_dataset; go CREATE PROC get_iris_dataset AS BEGIN EXEC sp_execute_external_script @language = N'R' , @script = N'iris_data <- iris;' , @input_data_1 = N'' , @output_data_1_name = N'iris_data' WITH RESULT SETS (("Sepal.Length" float not null, "Sepal.Width" float not null, "Petal.Length" float not null, "Petal.Width" float not null, "Species" varchar(100))); END; GO
B. Generate an R model based on data from SQL Server
The following example creates a stored procedure that uses sp_execute_external_script to generate an iris model and return the model to SQL Server.
This example requires advance installation of the e1071 package. For more information, see Install additional R packages on SQL Server.
DROP PROC IF EXISTS generate_iris_model; GO CREATE PROC generate_iris_model AS BEGIN EXEC sp_execute_external_script @language = N'R' , @script = N' library(e1071); irismodel <-naiveBayes(iris_data[,1:4], iris_data[,5]); trained_model <- data.frame(payload = as.raw(serialize(irismodel, connection=NULL))); ' , @input_data_1 = N'select "Sepal.Length", "Sepal.Width", "Petal.Length", "Petal.Width", "Species" from iris_data' , @input_data_1_name = N'iris_data' , @output_data_1_name = N'trained_model' WITH RESULT SETS ((model varbinary(max))); END; GO
To generate a similar model using Python, you would change the language identifier from
@language = N'Python', and make necessary modifications to the
@script argument. Otherwise, all parameters function the same way as for R.
C. Create a Python model and generate scores from it
This example illustrates how to use sp_execute_external_script to generate scores on a simple Python model.
CREATE PROCEDURE [dbo].[py_generate_customer_scores] AS BEGIN ## Input query to generate the customer data DECLARE @input_query NVARCHAR(MAX) = N'SELECT customer, orders, items, cost FROM dbo.Sales.Orders` EXEC sp_execute_external_script @language = N'Python', @script = N' import pandas as pd from sklearn.cluster import KMeans # Get data from input query customer_data = my_input_data # Define the model n_clusters = 4 est = KMeans(n_clusters=n_clusters, random_state=111).fit(customer_data[["orders","items","cost"]]) clusters = est.labels_ customer_data["cluster"] = clusters OutputDataSet = customer_data ' , @input_data_1 = @input_query , @input_data_1_name = N'my_input_data' WITH RESULT SETS (("CustomerID" int, "Orders" float,"Items" float,"Cost" float,"ClusterResult" float)); END; GO
Column headings used in Python code are not output to SQL Server; therefore, use the WITH RESULTS statement to specify the column names and data types for SQL to use.
For scoring, you can also use the native PREDICT function, which is typically faster because it avoids calling the Python or R runtime.
System Stored Procedures (Transact-SQL)
Python Libraries and Data Types
R Libraries and R Data Types
SQL Server R Services
Known Issues for SQL Server Machine Learning Services
CREATE EXTERNAL LIBRARY (Transact-SQL)
sp_prepare (Transact SQL)
external scripts enabled Server Configuration Option
SQL Server, External Scripts Object