ETL Processing Mechanics of ETL

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

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

Extract Customer data into a working table SELECT * INTO CustomerCopy FROM Customer;

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

Create a Surrogate Key Table CREATE TABLE CustomerSurrogates (CustomerNumber TEXT(3) CONSTRAINT pk PRIMARY KEY, Surrogate AUTOINCREMENT, CustomerKey Integer);

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);

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

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

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

Drop unnecessary columns ALTER TABLE CustomerCopy DROP balance;