Chapter 1 : Introduction

1
Chapter 1 Introduction

• BORDOLOI BOCK

2
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.

3
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.

4
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).

5
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.

6
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.

7
SQL

• SQL is used by Oracle for all interaction with
  the database. SQL statements fall into the two
  major categories
• Data Definition Language(DDL) Set of SQL
  commands that create and define objects in a
  database
• Data Manipulation Language(DML) Set of SQL
  commands that allow users to manipulate the data
  in a database.

8
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.

9
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.
  

10
Starting Oracle SQLPLUS

• The most common types used are either the
  standard Oracle SQLPLUS 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 SQLPLUS session is begun by typing the command
  sqlplus at the command prompt() and entering
  the username and password information .
• contd

11
Log On Screen



12
Exiting SQLPLUS

• The SQLPLUS 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 SQLPLUS
  session.

13
Running (Executing) a Command File

• The command to run (execute) a command file is
• SQLgt 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_ (at symbol).

14
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

15
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

16
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.

17
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.
• Identifiers should contain between 1 and 30
  characters.
• The first character must be either alphabetic
  (a-z, A-Z) or the _at_ symbol or _ (underscore).

18
SQL Naming Conventions

• After the first character, digits, letters, or
  the symbols ,, or _(underscore) must be used.
• No embedded spaces are allowed in identifiers.
• SQL keywords cannot be used as an identifier.