What Is a Relational Database

Saturday, March 21, 2009 · 0 comments







What Is a Relational Database?

The concept of a relational database was originally developed back in 1970 by Dr. E.F. Codd. He
laid down the theory of relational databases in his seminal paper entitled “A Relational Model of
Data for Large Shared Data Banks,” published in Communications of the ACM (Association for
Computing Machinery), Vol. 13, No. 6, June 1970.
The basic concepts of a relational database are fairly easy to understand. A relational database
is a collection of related information that has been organized into tables. Each table stores data in
rows; the data is arranged into columns. The tables are stored in database schemas, which are
areas where users may store their own tables. A user may grant permissions to other users so they can access their tables. Most of us are familiar with data being stored in tables

Introducing the Structured Query Language (SQL)

Structured Query Language (SQL) is the standard language designed to access relational
databases. SQL should be pronounced as the letters “S-Q-L.”
NOTE
“S-Q-L” is the correct way to pronounce SQL according to the American National Standards Institute. However, the single word “sequel” is frequently used instead.

SQL is based on the groundbreaking work of Dr. E.F. Codd, with the first implementation of
SQL being developed by IBM in the mid-1970s. IBM was conducting a research project known as System R, and SQL was born from that project. Later, in 1979, a company then known as Relational Software Inc. (known today as Oracle Corporation) released the first commercial version of SQL. SQL is now fully standardized and recognized by the American National Standards Institute. SQL uses a simple syntax that is easy to learn and use. You’ll see some simple examples of its use in this chapter. There are five types of SQL statements, outlined in the following list:
Query statements retrieve rows stored in database tables. You write a query using the
SQL SELECT statement.
Data Manipulation Language (DML)
statements modify the contents of tables. There are
three DML statements:
INSERT adds rows to a table.
UPDATE changes rows.
DELETE removes rows.

Data Definition Language (DDL) statements define the data structures, such as tables,
that make up a database. There are five basic types of DDL statements:

CREATE creates a database structure. For example, CREATE TABLE is used to create
a table; another example is CREATE USER, which is used to create a database user.

ALTER modifies a database structure. For example, ALTER TABLE is used to modify
a table.

DROP removes a database structure. For example, DROP TABLE is used to remove a
table.

RENAME changes the name of a table.

TRUNCATE deletes all the rows from a table.