intro to it chapter 6 db

8/14/2019 Intro to IT Chapter 6 Db

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DatabaseDatabase


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DatabaseDatabase Database is a collection of information in a structured

way

Example of database use are :- Banks

Travel Agent

Databases store information in fields, records, and files

A field is a single piece of informationa customers firstname, for example

A record is one complete set of fields the customersfirst name, last name, address, phone number, andaccount information. And

File is a collection of records a complete list of allcustomers.

Key Field is used to uniquely identify record for easyretrieval


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Database Storage HierarchyDatabase Storage Hierarchy

Type of dataType of data ContainsContains ExampleExample

DatabaseDatabase Several FilesSeveral Files PersonalPersonalDatabaseDatabase

FileFile Several RecordsSeveral Records Name1Name1Name2Name2

RecordRecord Several FieldsSeveral Fields ABDULLATIFABDULLATIFMIR, IST,MIR, IST,IslamabadIslamabadHighway nearHighway nearToll Plaza, IsbToll Plaza, Isb

FieldField Characters

Characters(bytes)(bytes)

First Name:First Name:ABDULLATIFABDULLATIF

CharactersCharacters Bits (0,1)Bits (0,1) Letter SLetter S1110 00101110 0010


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Database System ComponentsDatabase System Components

Hardware

Computer Peripherals

Software Operating Systems Software

DBMS Software People

Systems Administrators (SA) Database Administrators (DBAs) Database Designers / Programmers

End Users Data

Collection of facts stored in the database


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Types of Database SystemsTypes of Database Systems Number of Users

Single User Desktop Database

Multi User Workgroup Database IST

Enterprise Database NADRA

Scope Desktop

Workgroup

Enterprise

Location

Centralized Database IST Distributed Database e.g. ATM/DNS


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Examples of DatabaseExamples of Database


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Database ModelsDatabase Models A Database Model ordatabase schemais the

structure , format or way of arranging data

Six models are:-

Flat

HierarchalNetwork

Relational (most widely used)

Object OrientedMultidimensional


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File SystemFile System The file system that comes with computer is a very primitive

kind of database management system

Data are kept in big unstructurednamed clumps called files A flat file database is a database designed around a single table

The flat file design puts all database information in one table

A flat file may contain many fields, often, with duplicate datathat are prone to data corruption


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Hierarchical DatabaseHierarchical Database Hierarchical data model organizes related record/fields in a

tree structure There is a hierarchy ofparent and child data segments

Child may only have one parent but a parent can have multiplechildren

These database have well defined, pre specified accesspaths

Hierarchical structures were widely used in the early mainframedatabase management systems

Student

Name Address

CNIC Course GPA

CourseA

CourseB

Course CFirstName

LastName

Middle

Name

Exam2 Exam3Grade Exam 1Exam

2

Grade ExamExam

1 Grade


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Network Database ModelNetwork Database Model It is built upon Hierarchal database

Network model allows each data element to have multipleparent and child record i.e. each child record can havemore then one parent record

Child record can be reached through more then one parent

More flexible then Hierarchal database It is similar to Mesh network topology and allows quick retrieval

of data


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Relational Database ModelRelational Database Model The relational database stores information in tables

Table is made up ofrecords (horizontal rows also known astuples) and fields (vertical columns also known as attributes)

Each table is identified by a unique name and that name is usedby the database to find the table

Primary key is used to uniquely identify record with in table

Secondary key is used to link two tables SQL is used to search database

Record search is very fast because of primary key


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Object Oriented DatabaseObject Oriented DatabaseModelModel

A database system that incorporates all the important object-

oriented concepts It was designed to add database functionality to object

programming languages like Java , C++ etc

Database capabilities are combined with object-oriented (OO)programming language capabilities

This model store its contents as objects The main benefit of creating a database with objects as data is

speed

OQL is used to query database


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Database Management SystemDatabase Management System

(DBMS)(DBMS) Database Management System (DBMS), is collection of

software programs that let you to enter, organize, andselect information stored in the database e.g. Oracle,Microsoft SQL Server, MySQL etc.


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DBMS Vs File SystemsDBMS Vs File Systems Speed. Retrieval of data and application

development time Data Administration.You can administrate

the values being entered in the database byhaving various constraints on the data field.For example, you may allow only numericfields in salary field

Data Security. Database provide differentlevel of securities by having password toaccess different level of database whichis not provided with file systems (root user)

Concurrent Access. Multiple users can access

the database at a same time by using locksystem (yahoo mail)

Crash Recovery. In case your databasecrashes, it has a special mechanism by usingyou can recover your database on the

last saved state (RAID) Im roved Data Inte rit . Data is U to


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DBMS Vs File SystemsDBMS Vs File Systems

Problems

Costof software/hardware and migration

Complexity of backup and recovery

Skilled Manpowerrequired


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QueriesQueries Queries are the primary mechanism for retrieving

information from a database It consist ofquestions presented to the database in a

predefined format

Different ways to query database are :-

SQL (Structured Query Language) OLAP (online analytical processing) simple

language query

Data mining is a process of extracting hidden

trends within a data ware house. For examplean insurance data ware house can be used tomine data for the most high risk people toinsure in a certain geographical area


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SQLSQL SQL is structured query language for accessing and

manipulating database systems SQL works with database programs like MS Access,

DB2, Informix, MS SQL Server, Oracle, Sybase,etc.

almost everything can be accomplished by usingfollowing commands :-

Select Insert Update

Delete Create Drop


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Table BasicsTable Basics A relational database system contains one or more tables

The data or information for the database are stored in thesetables

Tables are uniquely identified by their names and are comprisedof columns and rows

Columns contain the column name, data type, and any otherattributes

Rows contain the records or data for the columns. Here is asample table called "weather". city, state, high, and low arethe columns. The rows contain the data for this table


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Data TypesData Types Data types specify what the type of data can be for

that particular column If a column called "Last_Name", is to be used to hold

names, then that particular column should have a"varchar" (variable-length character) data type

Here are the most common Data types


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Creating TablesCreating Tables The create tablestatement is used to create a new table Syntax :-

create table "tablename" ("column1" "data type","column2" "data type", "column3" "data type");

Example:- create table employee (first varchar(15), last

varchar(20), age number(3), address varchar(30),city varchar(20), state varchar(20));

Rules :- The table and column names must start with a

letter

not to exceed a total of30 charactersin length Do not use any SQL reserved keywords as names

for tables or column names (such as "select","create", "insert", etc)


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Drop a TableDrop a Table

The drop table statementis used to delete atable and all rows in the table

To delete an entire table including all of itsrows, issue the drop table commandfollowed by the table name

Dropping the table removes the tabledefinition as well as all of its rows

Syntax :- drop table "tablename" Example :- drop table myemployees_ts0211;


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Inserting into a TableInserting into a Table

The insert statement is used to insert or add arow of data into the table

Syntax :- insert into "tablename"

(first_column,...last_column) values(first_value,...last_value);

Example:- insert into employee (first, last, age, address,

city, state) values ('Luke', 'Duke', 45, '2130Boars Nest', 'Hazard Co', 'Georgia');

Note: All strings should be enclosed betweensingle quotes: 'string'


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Selecting DataSelecting Data The select statement is used to query the database

and retrieve selected data that match the criteriathat you specify

Syntax :-

select "column1" [,"column2",etc] from "tablename"[where "condition"];

The column names that follow the select keyworddetermine which columns will be returned in theresults. You can select as many column names thatyou'd like, or you can use a "*" to select all columns

The table name that follows the keyword fromspecifies the table that will be queried to retrievethe desired results


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Selecting DataSelecting Data The where clause (optional) specifies which data

values or rows will be returned or displayed, basedon the criteria described after the keyword where.

Conditional selections used in the where clause:

= Equal

> Greater than < Less than

>= Greater than

equal


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Updating RecordsUpdating Records The update statementis used to update or change

records that match a specified criteria. This is accomplished by carefully constructing a where

clause.

Syntax :-

update "tablename" set "columnname" = "newvalue"

[,"nextcolumn" = "newvalue2"...] where"columnname" OPERATOR "value" [and|or"column" OPERATOR "value"];

Examples:-

update phone_book set area_code = 623 where prefix =979;

update phone_book set last_name = 'Smith',prefix=555, suffix=9292 where last_name = 'Jones';

update employee set age = age+1 where

first_name='Mary' and last_name='Williams';


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Deleting RecordsDeleting Records The delete statementis used to delete records or rows from

the table Syntax:-

delete from "tablename where condition" Examples:

delete from employee; Note: if you leave off the whereclause, all records will be deleted!

delete from employee where lastname = 'May';

delete from employee where firstname = 'Mike' orfirstname = 'Eric';

To delete an entire record/row from a table, enter "delete from"followed by the table name, followed by the where clausewhich contains the conditions to delete. If you leave off thewhere clause, all records will be deleted.

intro to it chapter 6 db

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