Introduction to RDBMS & SQL

8/8/2019 Introduction to RDBMS & SQL

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Introduction to RDBMS & SQL


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Role of Data

Intelligent interpretation of data gives

information Information is vital to the success of an

organization

Not just information, it is right information at

the right time that makes a difference

A DBMS helps in obtaining this information


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Database Management Systems

What is a database system?

A database system is a computer-based record

keeping system whose overall purpose is to

record and maintain information.

It is an electronic filing cabinet.


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Benefits of DBMS

Data redundancy can be reduced

End to data inconsistencies

Enables data sharing

Standards can be set and followed

Data integrity is maintained Data security can be enforced


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Relational Database ManagementSystem

User tables Data

dictionary

Oracleserver


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Relational Database Properties

A relational database:

Can be accessed and modified byexecuting structured query language

(SQL) statements

Contains a collection of tables with no

physical pointers Uses a set of operators


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Entity-Relationship Model

Is based on object-based logical model

Comprises of entities and relationships Is essential to represent the relational

database


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Parts of an E-R Model

Entities - are anything which can be distinctly

identified, like a place, a person, data, aresult or a concept

Attributes - define special characteristics of

an entity

Relationships - can be defined as an

association between the entities


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E-R Diagrams

Are a graphical way of representing entities,

attributes and relationships Easy to understand by everyone

Offer an overview of the entire system


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Types of Relationships

One to One - A pair of tables where one

record from table1 points to one record intable2

One to Many - A pair of tables where one

record from table1 points to many records

in table2, BUT one record from table2points to only one record in table1


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Types of Relationships (Contd.)

Many to Many - Where one record from

table1 points to more than one record intable2 AND one record from table2 points to

more than one record in table1


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SQL Statements

Data Retrieval SELECT

Data Manipulation (DML) INSERT

DELETE

UPDATE

Data Definition (DDL) CREATE ALTER

DROP

RENAME


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Basic SELECT Statement

SELECT *|{column|expression [alias],...}

FROM table;

SELECT identifies whatcolumns

FROM identifies which table


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SELECT *FROM departments;

Selecting All Columns


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Selecting Specific Columns

SELECT department_id, location_id

FROM departments;


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Displaying Table Structure

Use the SQL*Plus DESCRIBE command to

display the structure of a table.

DESC[RIBE] tablename


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Limiting Rows Using a Selection

retrieve all employees

in department 90

EMPLOYEES


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Limiting the Rows Selected

Restrict the rows returned by using theWHERE clause.

The WHERE clause follows the FROM

clause.

SELECT *|{column|expression [alias],...}

FROM table

[WHERE condition(s)];


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Using theWHERE Clause

SELECT employee_id, last_name, job_id, department_id

FROM employees

WHERE department_id = 90 ;


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Comparison Conditions

Operator

=

>

>=

=10000

AND job_id =CLERK';


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Using the OROperator

ORrequires either condition to be true.ORrequires either condition to be true.

SELECT employee_id, last_name, job_id, salary

FROM employees

WHERE salary >= 10000

OR job_id =CLERK';


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SELECT last_name, job_id

FROM employees

WHERE job_idNOT IN ('IT_PROG', 'ST_CLERK', 'SA_REP');

Using the NOT Operator

Documents

Introduction to RDBMS & SQL