Summary
The five basic operations on tables are
- Select -- pick out rows
- Project -- pick out columns
- Union -- combine two tables with like attributes
- Difference -- remove items from one table based on another
- Product -- form new table with all pairs from two tables
Join is a powerful operation created from project/select
Database operations allow the DB to be set up to avoid redundancy, but allow the data to be exhibited to users in whatever form they want