How to pass two sql tables as input parameter for r codes in SQL Server

Question

I am running r codes in SQL Server. I have two tables in SQL Server database that I would like to pass as input data set into the R code. I can use @input_data_1

Answer 1

You can use R's built in serialization to accomplish this in the SQL Server 2016. It's definitely verbose, however, it does work.

Example, setup two separate input temp tables (they cannot be table variables, unfortunately):

 CREATE TABLE #Table1
    (
        [StrCol] NVARCHAR( 50 ),
        [IntCol] INT
    );

    INSERT INTO
        #Table1
        (
            [StrCol],
            [IntCol]
        )
        VALUES
        ( N'testing data 1', 1 ),
        ( N'testing data 2', 2 )
    ;

 CREATE TABLE #Table2
    (
        [StrCol] NVARCHAR( 50 ),
        [IntCol] INT
    );

    INSERT INTO
        #Table2
        (
            [StrCol],
            [IntCol]
        )
        VALUES
        ( N'more testing data 1', 5 ),
        ( N'more testing data 2', 6 )
    ;

From here, you can create VARBINARY types to hold the serialized results translated in R.

DECLARE
    @Table1_Input NVARCHAR( MAX ) = 'SELECT * FROM #Table1;',
    @Table2_Input NVARCHAR( MAX ) = 'SELECT * FROM #Table2;',
    @Table1_Data VARBINARY( MAX ),
    @Table2_Data VARBINARY( MAX );

EXECUTE sp_execute_external_script
    @language = N'R',
    @script = N'

        if( nrow(InputDataSet) == 0 )
            stop("Invalid data passed in")

        # Read in the sql table, serialize it to an output string
        Output <- serialize(InputDataSet, NULL)
    ',
    @input_data_1 = @Table1_Input,
    @params = N'@Output VARBINARY( MAX ) OUTPUT',
    @Output = @Table1_Data OUTPUT;

EXECUTE sp_execute_external_script
    @language = N'R',
    @script = N'

        if( nrow(InputDataSet) == 0 )
            stop("Invalid data passed in")

        # Read in the sql table, serialize it to an output string
        Output <- serialize(InputDataSet, NULL)
    ',
    @input_data_1 = @Table2_Input,
    @params = N'@Output VARBINARY( MAX ) OUTPUT',
    @Output = @Table2_Data OUTPUT;

Finally,

EXECUTE sp_execute_external_script
    @language = N'R',
    @script = N'

        table1 <- unserialize(Table1_Data)
        table2 <- unserialize(Table2_Data)

        OutputDataSet <- rbind(table1, table2)
    ',
    @params = N'@Table1_Data VARBINARY(MAX), @Table2_Data VARBINARY(MAX)',
    @Table1_Data = @Table1_Data,
    @Table2_Data = @Table2_Data
    WITH RESULT SETS (( [Col1] NVARCHAR( 50 ), [Col2] INT ));

Results:

Col1    Col2
testing data 1
testing data 2
more testing data 5
more testing data 6