what is database

A database is a structured collection of data.

Often abbreviated DB. A collection of information organized in such a way that a computer program can quickly select desired pieces of data. You can think of a database as an electronic filing system.

Traditional databases are organized by fields, records, and files. A field is a single piece of information; a record is one complete set of fields; and a file is a collection of records. For example, a telephone book is analogous to a file. It contains a list of records, each of which consists of three fields: name, address, and telephone number.

An alternative concept in database design is known as Hypertext. In a Hypertext database, any object, whether it be a piece of text, a picture, or a film, can be linked to any other object. Hypertext databases are particularly useful for organizing large amounts of disparate information, but they are not designed for numerical analysis.

To access information from a database, you need a database management system (DBMS). This is a collection of programs that enables you to enter, organize, and select data in a database.

The following figure shows the basic layout of a database table:

A column defines one piece of data stored in all rows of the table. A row contains one item from each column in the table.

For example, a table might contain the ID, name, title, and other information for individuals employed by a company. Each row, called a data record, corresponds to one employee. The value of a column within a record is referred to as a record field.

The following figure shows an example table, named employees, containing information about company employees:

The record for employee 4 contains the following field values:

• LastName field is "Smith"
• FirstName field is "John"
• Title field is "Engineer"

This example uses the EmpID field as the table's primary key field. The primary key contains a unique identifier to maintain each record's unique identity. Primary keys field can include an employee ID, part number, or customer number. Typically, you specify which column contains the primary key when you create a database table.

To access the table to read or modify table data, you use the SQL programming language. For example, the following SQL statement returns all rows from the table where the department ID is 3:

SELECT * FROM employees WHERE DEPTID=3