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 CustomerCopy
FROM Customer;

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 CustomerSurrogates
(CustomerNumber TEXT(3)
CONSTRAINT pk PRIMARY KEY,
Surrogate AUTOINCREMENT,
CustomerKey Integer);

7. Insert primary keys into the surrogate key table and generate surrogate keys.
INSERT INTO CustomerSurrogates (CustomerNumber)
SELECT CustomerNumber FROM CustomerCopy
WHERE CustomerNumber
NOT IN (SELECT CustomerNumber FROM CustomerSurrogates);

8. Copy the autonumber field into an integer field.
UPDATE CustomerSurrogates
SET CustomerKey = Surrogate
WHERE CustomerKey IS Null ;

9. Add a CustomerKey column to the CustomerCopy table
ALTER TABLE CustomerCopy ADD COLUMN CustomerKey NUMBER;

10. Update the CustomerCopy table to add surrogate keys.
UPDATE CustomerCopy, CustomerSurrogates
SET CustomerCopy.CustomerKey = CustomerSurrogates.CustomerKey
WHERE CustomerCopy.CustomerNumber = CustomerSurrogates.CustomerNumber;

11. Drop unnecessary columns
ALTER TABLE CustomerCopy
DROP balance;