1. ETL Processing
Mechanics of ETL

2. The Flow Source File Extract Transform Transformed File Extract
Generate
Key
Presentation
Mart
Surrogate Keys

3. The Flow Customer Extract Transform Transformed File CopyCustomer
Generate
Key
Presentation
Mart
NewTable

4. Extract Customer data into a working table
SELECT * INTO SalesCopy
FROM Sales;

5. Add Surrogate Keys
Create a table with primary key and surrogate key attributes, transaction primary key as primary key and autoincrement for a new surrogate key

6. Create a Surrogate Key Table
create table surrogate (
keyval int
constraint pk primary key,
Autokey int identity(1,1),
Surrogate int)

7. Insert primary keys into the surrogate key table and generate surrogate keys.
INSERT INTO Surrogate (KeyVal)
SELECT KeyVal FROM Sales
WHERE KeyVal
NOT IN (SELECT KeyVal FROM Surrogate);

8. Copy the autonumber field into an integer field.
UPDATE Surrogate
SET Surrogate= autokey
WHERE surrogate is null

9. Add a CustomerKey column to the CustomerCopy table
ALTER TABLE Sales
ADD SalesKey Int;

10. Update the CustomerCopy table to add surrogate keys.
UPDATE sales
SET sales.saleskey = surrogate.surrogate
FROM sales, surrogate
WHERE sales.keyval = surrogate.keyval

11. Drop unnecessary columns
ALTER TABLE CustomerCopy
DROP balance;