Table “selection” means that all or some of the table rows can be retrieved into the result table.

Selected Result Table:

Table “projection” means that all or just some of the table columns can be retrieved into the result table.

Projected Result Table:

Relational Database Management Systems get their power and simplicity from “Set Theory” which was invented in the eighteenth century. Possibly you remember doing “Joins” and “Unions” in college. Now you will be able to put that theory to good, practical use. You will be joining two or more tables using SQL. A single SQL statement can also insert, update, or delete many rows of data all at one time.