Download Chapter 1 : Introduction

Chapter 1 : Introduction
BORDOLOI & BOCK
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SQL
• SQL, pronounced ‘Sequel’ or simply S-Q-L, is a
computer programming language that was
developed especially for querying relational
databases using a non-procedural approach.
• The term non-procedural means that you can
extract information by simply telling the system
what information is needed without telling how to
perform the data retrieval. The RDBMS parses
(converts) the SQL commands and completes the
task.
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SQL
• Extracting information from the database by
using SQL is termed querying the database.
• SQL is a language that is fairly simple to learn,
in terms of writing queries but it has
considerable complexity because it is a very
powerful language.
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DATA AND INFORMATION
• Information is derived from raw facts known as
data.
• Data has little meaning or usefulness to managers
unless it is organized in some logical manner.
• One of the most efficient ways to organize and
manage data is through the use of database
management system (DBMS).
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DATA
•
Two types of data are stored within a database
•
User data : Data that must de stored by an
organization.
System data: Data the database needs to
manage user data to manage itself. This is
also termed metadata, or the data about data.
•
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SQL
• Data is manipulated by RDBMS users through
the use of special data manipulation language.
• Database structures can also be defined by the
use of data definition language.
• SQL is the most popular database language and
has commands that enable it to be used for both
manipulation and definition of databases.
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SQL
•
SQL is used by Oracle for all interaction with
the database. SQL statements fall into the two
major categories
1. Data Definition Language(DDL) : Set of SQL
commands that create and define objects in a
database
2. Data Manipulation Language(DML) : Set of
SQL commands that allow users to
manipulate the data in a database.
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SQL
• SQL is basically a free format language. This
means that there are no particular spacing rules
that must be followed when typing SQL
commands.
• In Oracle, you must end each individual
SQL statement (irrespective of whether it is
composed as a single or multiple lines of
code) with a semi-colon (;). It is the “;”
which ends an SQL statement and tellls
Oracle to Execute it.
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RELATIONAL OPERATIONS
• SQL operations for creating new tables,
inserting table rows , updating table rows,
deleting table rows, and querying databases are
the primary means of interfacing with relational
databases.
• The SELECT statement is used primarily to
write queries that extract information from the
database which is a collection of related tables.
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Starting Oracle SQL*PLUS
•
•
•
The most common types used are either the
standard Oracle SQL*PLUS available for a
Windows-type interface or by connecting to an
Oracle database via a telnet session.
The following Log On session is a connection to
an Oracle database stored on a Sun Microsystems
server running the Unix O/S.
A SQL*PLUS session is begun by typing the
command sqlplus at the command prompt($) and
entering the username and password information .
contd
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Log On Screen
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Exiting SQL*PLUS
•
•
The SQL*PLUS session can be ended by
typing a command at the SQL prompt to
terminate the session.
Two commands are available: exit or quit.
Either one of these can be used to terminate a
SQL*PLUS session.
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Running (Executing) a Command File
•
The command to run (execute) a command file
is:
SQL> START filename.sql
•
A form of shorthand for the word “start” can be
used when executing a command file by
replacing “start” with the @ (“at” symbol).
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Syntax Conventions
•
•
Each select statement must follow precise
syntactical and structural rules.
The following is the minimum structure and
syntax required for an SQL SELECT statement.
SELECT [DISTINCT | ALL] {* |
select_list}
FROM {table_name [alias] | view_name}
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SQL Keywords
•
•
Keywords are words that have a predefined
meaning in SQL.
In practice, keywords may be entered in upper
or lower case letters.
SELECT *
FROM employee;
select *
from employee;
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SQL Keywords
•
•
In some cases keywords can be abbreviated.
The allowed abbreviation is shown in upper
case letters with the remainder shown in lower
case, which means either the full word or only
the upper case part can be used.
DESCribe: can be entered as either DESC or
DESCRIBE.
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SQL Naming Conventions
•
Identifiers are the names given by information
system developers or system users to database
objects such as tables , columns, indexes, and
other objects as well as the database itself.
• There are several rules for naming database
objects that must be followed.
1. Identifiers should contain between 1 and 30
characters.
2. The first character must be either alphabetic (az, A-Z) or the @ symbol or _ (underscore).
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SQL Naming Conventions
3. After the first character, digits, letters, or the
symbols $,#, or _(underscore) must be used.
4. No embedded spaces are allowed in identifiers.
5. SQL keywords cannot be used as an identifier.
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