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.

Logical tables are called views.

Here is a sample base table with column headings:

Here is a view table:

> No data is stored in a view because it is a virtual table.
The data is actually in one or more base tables.

> A view is always a single table, no matter how many
tables are the source of the view data.

> The view definition is stored in the system catalog.

> Specific columns or rows may be excluded from the view.

> A view can be used for security purposes.