ey would no longer be unique. Sometimes the design team has to define a new ID number or code field, just so that a table has a primary key. For the EMPLOYEE table, the primary key would likely be the employee ID number. Once a table has been assigned a primary key, Oracle won't allow more than one record in the table with the same value for the primary key. No two employees can have the same ID number. Relational DatabasesSometimes all the information of interest to a business operation can be stored in one table. For example, let's say the only data you need to maintain about your office supplies is a description of each item, its supplier, and the quantity on hand. It would be enough to have one office supply table with those data items as the fields. More often, though, business applications involve many tables. In a typical personnel application, there might be one table for employees, another for information about their hours of work, and another for the departments in the company. Oracle makes it very easy to link the data in multiple tables: matching an employee to the department in which they work is one example. This is what makes Oracle a relational database management system, or RDBMS. It stores data in two or more tables and enables you to define relationships between the tables. The link is based on one or more fields common to both tables. For example, the following diagram represents part of the EMPLOYEE table and the entire DEPARTMENT table: +-----------------------------+ +-------------------------------------+| EMPLOYEE | | DEPARTMENT |+---------+------------+------+ +---------+----------------+----------+| EMPL_ID | NAME_LAST | DEPT | | DEPT_NO | DESCRIPTION | LOCATION |+---------+------------+------+ +---------+----------------+----------+| 1 | Slate | 1 | | 1 | Administration | Bedrock || 4 | Flintstone | 2 |...
