Create View in Polybase

Question

I am trying to load multiple files via polybase and its throwing me an error while creating view.

select * from dbo.test

fname lname
a.csv null
b.csv null

I am able to successfully create data source and external table without any issue.

Code Error

Error in the code.
Msg 207, Level 16, State 1, Line 4
Invalid column name 'DATA_FILE_NAME'.
Invalid column name 'DATA_FILE_NAME'.
Invalid column name 'DATA_FILE_NAME'.
Invalid column name 'DATA_FILE_NAME'.
Invalid column name 'DATA_FILE_NAME'.
Invalid column name 'DATA_FILE_NAME'.
Invalid column name 'DATA_FILE_NAME'.
Invalid column name 'DATA_FILE_NAME'.
Invalid column name 'DATA_FILE_NAME'.
Invalid column name 'DATA_FILE_NAME'.

CODE

 IF OBJECT_ID('dbo.TEST_V', 'V') IS NOT NULL
DROP VIEW [dbo].[TEST_V]
GO

 -- Create new view
CREATE VIEW [dbo].[TEST_V]
AS

-- Add dynamic T-SQL to temporary table 

SELECT 

-- Auto increment number
ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS ROW_ID,

-- Data file name
DATA_FILE_NAME AS DATA_FILE,

-- Drop external table if it exists
'IF EXISTS (SELECT * FROM sys.external_tables WHERE NAME = ' + 
CHAR(39) + SUBSTRING(DATA_FILE_NAME, 1, LEN(DATA_FILE_NAME) - 11) + CHAR(39) + ') ' + 
'DROP EXTERNAL TABLE [dbo].[' + SUBSTRING(DATA_FILE_NAME, 1, LEN(DATA_FILE_NAME) - 11) + '];' AS DROP_STMT,

-- Create new external table
'CREATE EXTERNAL TABLE [dbo].[' + SUBSTRING(DATA_FILE_NAME, 1, LEN(DATA_FILE_NAME) - 11) + '] ' + 
'( ' + 
'fname [varchar] (70), ' +
'lname [varchar] (70) ' +
   ') ' + 
'WITH ' +
'( ' +
'LOCATION=' + CHAR(39) + '/NEW/' + DATA_FILE_NAME + CHAR(39) + ' ' +
', DATA_SOURCE = SIMPLE' +
', FILE_FORMAT = SIMPLE_HEADER' +
', REJECT_TYPE = VALUE ' + 
', REJECT_VALUE = 1 ' +
') ' AS CREATE_STMT,

-- Move data into staging table
'INSERT INTO dbo.fname ' + 
'SELECT ' +
'  fname ,' +
'  lname ' +
'FROM [dbo].[' + SUBSTRING(DATA_FILE_NAME, 1, LEN(DATA_FILE_NAME) - 11) + '] ' +
';' AS INSERT_STMT

FROM 
[dbo].[test];
GO

I am trying to create procedure using the above view to load data using multiple files dynamically.

Answer 1

Since they are all targeting the same table, you don't need to use this file-by-file method. Polybase will load a wildcard-like set of files. If you put all your data files of the same type in a folder, and set the FOLDER as the location, all the files in the folder will be loaded in parallel. You will find your loads hugely faster … at the moment you're processing files in series, using the method I suggest will process them in parallel as fast as readers are available.