In a data warehouse environment, there’s often a separate database used by the ETL process that's typically called the staging database. The tables in this database might bear little to no resemblance to the tables in the final data warehouse; some are landing places for transactional and non-transactional datasources as they enter the data warehouse environment.

Other tables are used as intermediate steps in the checking, scrubbing, separating, decoding, validating, and verifying portions of the ETL process. Still other tables are used to store operational audit logs.

Typically, indexing these tables is severely limited, to the point in which some tables have no indexes on them at all. Instead, data integrity is managed and maintained by the transformation process. I'll discuss some of the transformation process in a future article.