DBMSMIS BBA(Hons) 8th Lec 192021

8/7/2019 DBMSMIS BBA(Hons) 8th Lec 192021

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DBMS & MIS

BBA (Hons) 8th

(Lectures 16,17,18)

Databases: The Technical Stuff

Course Lecturer: Farhan Mir


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Relational Databases. Independent Tables

Relationship through primary & secondarykeys

SQL Select: Creates subset of rows that meet specific criteria Join: Combines relational tables to provide users with

information

Project: Enables users to create new tables containingonly relevant information

Compatibility with Existing Applications Database Security

Data Dictionaries


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What Makes a Database Relational?

A database is relational when files are

related to each other, such as this Student ID

field in the Student file.


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Relational Database

Data stored in related tables

Table records have same record type

Record = table row

Attributes = table columns (fields) Uses common key fields for relationships


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Table and Record Example


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Database Characteristics

Relationship: association between data

stored in different tables


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Designing Databases

Database structure: arrangement of the

fields, tables and relationships

Design for ease of access and

maintenance in as small a file as possible. First determine what data must be collected

and stored

Next organize data into fields and define how

the field is stored Break data into small fields (firstname,

lastname)


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Data Types

Character

Numeric Real and integer

Date Logical

Memo

Image

Calculated field


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Organizing Table Data

Sort order: order in which records are

stored on disk

Queries and updates are faster Sort key (one or more fields)

Database index: list of keys and

associated record numbers

Doesnt affect the way records are physically

stored


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Lets have a closer look at

Structured query language

SQL


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SQL basics

SQL allows you to access a database

SQL executes queries against a database

SQL commands are case independent.

SELECT = select

But column names or DATA are not case independent.

SQL command are named after english words:

Create, select, insert, update ...

It's easy to learn


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3 types of SQL commands

1. Data Definition Language (DDL) commands - thatdefine a database, including creating, altering, and

dropping tables and establishing constraints 2. Data Manipulation Language (DML) commands - thatmaintain and query a database

3. Data Control Language (DCL) commands - thatcontrol a database, including administering privileges

and committing data


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Syntax used in these notes

Capitals = command syntax

Lowercase = values that must be supplied by user

Brackets = enclose optional syntax

Each SQL command ends with a semicolon ; In interactive mode, when the user presses the RETURN

key, the SQL command will execute


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Data Definition Language: create the tables

Create table syntax

CREATE TABLE tablename (

column1 data_type [not null] [unique] [column_constraint] ,

...

[table constraints]);

Example:

CREATE TABLE person (personID varchar(5) NOT NULL,

Name varchar(25) NOT NULL,

Firstname varchar(15) NULL);


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How to judge which table to

create and what could be thecolumns (fields)


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Remember from the Production System

Case Study: you are transforming an Entity to a Table


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Simple entity translation

General Rule:

Create a table with the name of the Entity. There is a column for each attribute

The key in the diagram is the primary key of the

table

Actorid

name address

birthday


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student

id

name

address

id name address

Student


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How to Create tables with SQL

The columns needed for each table can be defined using

the CREATE TABLE command. The syntax for this is

shown in the upcoming figure. These are the seven

steps to follow:

1. Identify the appropriate datatype for each columns,

including length and precision

2. Identify those columns that should accept null values.

Column controls that indicate a column cannot be null

are established when a table is created and are enforcedfor every update of the table


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Creating tables

3. Identify those columns that need to be UNQUE - when

the data in that column must have a different value (no

duplicates) for each row of data within that table. Where

a column or set of columns is designated as UNIQUE,

this is a candidate key. Only one candidate key may be

designated as a PRIMARY KEY

4. Identify all primary key-foreign key mates. Foreign

keys can be established immediately or later by altering

the table. The parent table in such a parent-childrelationship should be created first. The column

constraint REFERENCES can be used to enforce

referential integrity


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Creating tables

5. Determine values to be inserted into any columns for

which a DEFAULT value is desired - can be used to

define a value that is automatically inserted when no

value is provided during data entry.

6. Identify any columns for which domain specifications

may be stated that are more constrained than those

established by data type. Using CHECK it is possible to

establish validation rules for values to be inserted into

the database 7. Create the table and any desired indexes using the

CREATE TABLE and CREATE INDEX statements


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Simple entity translation and creating table

create table Actor(id varchar(20) primary key,name varchar(40),

birthday date,

address varchar(100));

Actorid

name address

birthday

Relation: Actor (id, name, birthday, address)


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Table creationGeneral syntax for CREATE TABLE


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Table creation

The following Fig. Shows SQL database definition

commands

Here some additional column constraints are shown, and

primary and foreign keys are given names For example, the CUSTOMER tables primary key is

CUSTOMER_ID

The primary key constraint is named CUSTOMER_PK,

without the constraint name a system identifier would be

assigned automatically and the identifier would be

difficult to read


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SQL database definition commands for Pine Valley Furniture


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The final shape of the DDL in this case

Overall table

definitions


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Constraints

NOT NULL : the column cannot take the

NULL value

NULL : the column can take the null value

(default)

UNIQUE : the column has unique values


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Example

CREATE TABLE person (

personID varchar(5) NOT NULL UNIQUE,

Name varchar(25) NOT NULL,

Firstname varchar(15) NULL,

City varchar(20)


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DDL: alter table

Modifying the structure of a table. Add a

column:

ALTER TABLE ADD [DEFAULT

] []


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DDL: drop table

Delete a table

DROP TABLE tablename;

It is very easy and fast to type the drop

table command -> be careful !!!


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Data Manipulation Language (DML):

Update Operations

INSERT - inserts a list of attributes .

INSERT INTO PERSON VALUES (008, Tome, Hector, J);

DELETE - removes a row from a table.DELETE FROM PERSON WHERE ID = 7;

Attention DELETE FROM PERSON will delete

the whole table


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UPDATE - changes the value of one or

more attributes in a row.

When modifying an attribute that is not a

primary key or foreign key, there is usually

no danger of violating a constraint.

When modifying a primary key, it is

equivalent to doing a delete followed by aninsert operation.

UPDATE PERSON SET ID = 007 WHERE

LastName=Tome AND FirstName=Pat;

Update Operations


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Select

Select is used to retrieve data :

SELECT [DISTINCT]

FROM

[WHERE ]

[ORDER BY ]

In uppercase are the SQL keywords Between [] optional conditions

Between what correspond to your table(s) definition


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Select all data

SELECT FIRSTNAME, SURNAME

FROM PERSON

Select specific data, ordered

SELECT FIRSTNAME, SURNAME FROM PERSON WHERE

SURNAME = BONDORDER BY FIRSTNAME ASC

FirstName SurName

JAMES KIRK

JAMES BOND

... ...

Select


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Select all data where person firstname begins with

JAM

SELECT * FROM PERSON WHERE FIRSTNAME like 'JAM%'

PersonID FirstName SurName MidInitial

045 JAMES KIRK T007 JAMES BOND X


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More examples: special conditions

Set conditions: [ ] IN ()

SELECT firstname FROM person WHERE

surname IN ('BOND','KIRK');

DBMSMIS BBA(Hons) 8th Lec 192021

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