Table design

You use tables to store and organize data in the database. A table contains columns and rows. For example, the following is an example of how a Customer table might look. Each row in the Customer table represents an individual customer. The column contains information that describes the data for the individual customer. Each column has a data type, which identifies a format in which the data is stored in that column. Some data types can have a fixed length, which means that the size does not depend on the data stored in it. You also have data types with variable lengths, which means their length changes to fit the data they possess.

Entities are business objects that your database contains, and they are used to logically separate the data in the database. An entities list, which you need to create, is used to determine the tables as part of the physical design phase. You create a separate table in the database for each entity (such as customers, employees, orders, and the payroll). Entities are characterized by attributes. For example, you declare each individual attribute of an entity (such as an individual customer, an individual order, an individual employee, or an individual payroll record) as a row in the table.

An attribute is a property of an entity. For example, the employee entity has attributes such as the employee ID, first name, last name, birthday, social security number, address, country, and so on. Some attributes are unique values. For example, each customer in a Customer table has a unique customer number. Attributes are used to organize specific data within the entity.