Page 8 - DCAP508_DATABASE_ADMINISTRATION

Database Administration

Notes 1.1 What is SQL?

SQL is a tool for organizing, managing, and retrieving data stored by a computer database. The
acronym SQL is an abbreviation for Structured Query Language. For historical reasons, SQL is
usually pronounced “sequel,” but the alternate pronunciation “S.Q.L.” is also used. As the name
implies, SQL is a computer language that you use to interact with a database. In fact, SQL works
with one specific type of database, called a relational database.
Figure 1.1: Use of SQL for Database Access

Figure 1.1 shows how SQL works. The computer system in the figure has a database that stores
important information. If the computer system is in a business, the database might store
inventory, production, sales, or payroll data. On a personal computer, the database might store
data about the checks you have written, lists of people and their phone numbers, or data extracted
from a larger computer system. The computer program that controls the database is called a
database management system, or DBMS.
When you need to retrieve data from a database, you use the SQL language to make the request.
The DBMS processes the SQL request, retrieves the requested data, and returns it to you. This
process of requesting data from a database and receiving back the results is called a database
query—hence the name Structured Query Language.

Notes The name Structured Query Language is actually somewhat of a misnomer. First of
all, SQL is far more than a query tool, although that was its original purpose, and retrieving
data is still one of its most important functions.

SQL is used to control all of the functions that a DBMS provides for its users, including:
1. Data definition: SQL lets a user define the structure and organization of the stored data
and relationships among the stored data items.

2. Data retrieval: SQL allows a user or an application program to retrieve stored data from
the database and use it.
3. Data manipulation: SQL allows a user or an application program to update the database
by adding new data, removing old data, and modifying previously stored data.
4. Access control: SQL can be used to restrict a user’s ability to retrieve, add, and modify data,
protecting stored data against unauthorized access.

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