WHERE DOES SQL FIT IN?
With SQL you create new data, delete old
data, modify existing data, and retrieve data
from a relational database. The following
statement, for example, creates a new
EMPLOYEE table:
CREATE TABLE employee
(employee_id NUMBER,
first_name VARCHAR2( 30),
last_name VARCHAR2( 30),
hire_date DATE,
salary NUMBER( 9, 2),
manager NUMBER);
Note that this statement creates a table with
the names of each column (aka data attribute) and each column’s respective datatype
and length. For example, this line of the
CREATE TABLE statement:
employee_id NUMBER
creates a table column (data attribute) called
EMPLOYEE_ID with a datatype of NUMBER.
This EMPLO YEE_ID column is therefore
defined to contain only numeric data
The SQL SELECT statement enables you
to retrieve, or query, data. For example,
the following SQL statement retrieves all
FIRS T_NAME, LAST_NAME, and HIRE_
DATE column values from this article’s
EMPLOYEE table:
SELECT first_name, last_name, hire_date
FROM employee;
As you can see, the syntax is fairly
straightforward.
CONCLUSION
This article introduced the organization and
structure of a relational database. It described
tables, columns, and rows and presented
examples of data and how it is represented in
a relational database. The next article in this
SQL 101 series will continue the discussion
of data normalization and introduce the SQL
execution environment. T
Melanie Caffrey is
a senior development
manager at Oracle.
Caffrey is a coauthor
of Expert PL/SQL
Practices for Oracle
Developers and DBAs (Apress, 2011).
NEXT STEPS
READ more about relational database design
and concepts
Oracle Database Concepts 11g Release 2 ( 11. 2)
bit.ly/aonqPP
Oracle Database SQL Language Reference 11g
Release 1 ( 11. 1)
bit.ly/jYXQZn
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