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Practical T-SQL
Lesson 57. Loading Large CSVs Into Data Warehouse Staging Tables
When I load large CSVs into staging, I want to use BULK INSERT. The problem with BULK INSERT is that it will not load a file into a table that does not match the schema of the file. That is problematic as staging tables have audit columns that certainly will not be in the file. This is the process I use to get around this problem.
  1. 1.
    In your load proc, remove all keys and indexes from the target table. Those things slow down the load.
  2. 2.
    Create a view of the target table with the exact same name as the target table and place it in the dbo schema. The view should only contain those columns in the file.
  3. 3.
    Use BULK INSERT to load the view which will load the table. Set the parameters of BULK INSERT to fit the scenario.
  4. 4.
    In your load proc, add back all the keys and indexes.

Examples

Comprehensive Load Example
We are going to use the sample dataset "Flights Table From the nycflights13 Dataset".
In [ ]:
USE demo
DROP TABLE IF EXISTS temp.FlightsStaging
DROP SCHEMA IF EXISTS temp
DROP VIEW IF EXISTS FlightsStaging
GO
CREATE SCHEMA temp
CREATE TABLE temp.FlightsStaging(
ETLKey uniqueidentifier NOT NULL,
year NVARCHAR(255) NULL,
month NVARCHAR(255) NULL,
day NVARCHAR(255) NULL,
dep_time NVARCHAR(255) NULL,
sched_dep_time NVARCHAR(255) NULL,
dep_delay NVARCHAR(255) NULL,
arr_time NVARCHAR(255) NULL,
sched_arr_time NVARCHAR(255) NULL,
arr_delay NVARCHAR(255) NULL,
carrier NVARCHAR(255) NULL,
flight NVARCHAR(255) NULL,
tailnum NVARCHAR(255) NULL,
origin NVARCHAR(255) NULL,
dest NVARCHAR(255) NULL,
air_time NVARCHAR(255) NULL,
distance NVARCHAR(255) NULL,
hour NVARCHAR(255) NULL,
minute NVARCHAR(255) NULL,
time_hour NVARCHAR(255) NULL,
UniqueDims varbinary(35) NULL,
UniqueRows varbinary(16) NULL,
SourceSystem nvarchar(255) NULL,
Cleansed bit NULL,
ErrorRecord bit NULL,
ErrorReason nvarchar(255) NULL,
Processed bit NULL,
RunDate datetime NULL,
CONSTRAINT PK_FlightsStaging PRIMARY KEY CLUSTERED
(
[ETLKey] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE temp.FlightsStaging ADD CONSTRAINT DF_FlightsStaging_ETLKey DEFAULT (newid()) FOR ETLKey
GO
ALTER TABLE temp.FlightsStaging ADD CONSTRAINT DF_FlightsStaging_SourceSystem DEFAULT (N'Flights System') FOR SourceSystem
GO
ALTER TABLE temp.FlightsStaging ADD CONSTRAINT DF_FlightsStaging_Cleansed DEFAULT ((0)) FOR Cleansed
GO
ALTER TABLE temp.FlightsStaging ADD CONSTRAINT DF_FlightsStaging_ErrorRecord DEFAULT ((0)) FOR ErrorRecord
GO
ALTER TABLE temp.FlightsStaging ADD CONSTRAINT DF_FlightsStaging_Processed DEFAULT ((0)) FOR Processed
GO
ALTER TABLE temp.FlightsStaging ADD CONSTRAINT DF_FlightsStaging_RunDate DEFAULT (getdate()) FOR RunDate
GO
CREATE VIEW FlightsStaging
AS
SELECT
year,
month,
day,
dep_time,
sched_dep_time,
dep_delay,
arr_time,
sched_arr_time,
arr_delay,
carrier,
flight,
tailnum,
origin,
dest,
air_time,
distance,
hour,
minute,
time_hour
FROM temp.FlightsStaging
GO
--Begin Load
ALTER TABLE temp.FlightsStaging DROP CONSTRAINT PK_FlightsStaging WITH ( ONLINE = OFF )
GO
--Insert into the view
BULK INSERT FlightsStaging
FROM 'E:\flights.csv'
WITH (
FIELDTERMINATOR = ',',
ROWTERMINATOR = '0x0a',
FIRSTROW = 2
);
ALTER TABLE temp.FlightsStaging ADD CONSTRAINT PK_FlightsStaging PRIMARY KEY CLUSTERED
(
ETLKey ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
--but the records went to the actual table
SELECT *
FROM temp.FlightsStaging
DROP TABLE temp.FlightsStaging
DROP SCHEMA temp
DROP VIEW FlightsStaging
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