web programming course, winter 2005 database & sql introduction web programming course...

Web programming course, Winter 2005

Database & SQL introduction

Web Programming course

Acknowledgement : this presentation uses examples from the w3c website; available at - http://www.w3schools.com


Outline

Database introductionMotivationHistory Implementation

SQL introduction


Utility of Databases

Data have value independent of use Organized approach to data management

(e.g., data mining) Advantages

Eliminate redundancy in data Share data Archive data Security of data Integrity of data


DEFINITION

A collection of application programs that perform services to end users.

Each program defines and manages its own data.

File Based Systems


Data Entry& Reports

File handlingRoutines

File Definition

Sales Files

Data Entry& Reports

File handlingRoutines

File Definition

Lease Files

File Based Processing

physical structure and storage of the data files are defined in the program code


Data Dependence Duplication of Data Incompatible file formats

Limitations of File Based Systems

How can these problems be resolved?


A shared collection of logically

related data designed to meet the

information requirements of an

organisation

The Database Approach


Data Entry& reports

Data Entry& reports

DBMSSales

Leases

ApplicationPrograms

App. Programs

Database

Database Processing


DEFINITION A software system that enables users to

define, create and maintain the database and which provides controlled access to the database

Database Management System (DBMS)


Allows users to define the database (DDL)

Allows users to insert, update, delete & retrieve data (DML)

Provides controlled accessa security systeman integrity systema concurrency control systema recovery system

Facilities of a DBMS

What does it mean to define a database?


Hardware Software Data Procedures People

Components of a DBMS


Minimal data redundancy Consistency of data Integration of data Improved integrity Consistent security Standards Increased productivity

Advantages


Complexity Additional Hardware Costs Size Performance Experts -Specialised Personnel Potential organisational Conflict Higher impact of failure (centralized

data source failure)

Disadvantages


Database Interfaces

web server &interface prog

relationaldatabase

web browser

dedicated applicationSQL command interface

SQL

SQL SQL


Interaction and Feedback

Transaction: non-decomposable unit of data manipulation example: purchasing an airline ticket on-line typically small and fast for commercial applications may be long and involved in engineering applications

Rollback: if any part of a transaction fails, all completed parts are “rolled back” or undone example: if you haven’t provided your credit card number,

airline ticket purchase on-line transaction fails rollback ensures integrity of database automatically done by DBMS


Relational Database Model Database

Database is a collection of tables (relations) Data are stored in tables

Tables Each table has a name Each table has a set of columns (fields) and rows of data

(records) All operations process a table to produce a new table Each table has a fixed number of columns Each table has an arbitrary number of rows

Based on set theory SQL (Structured Query Language)

DBMS independent language

Why?


Weather Sample TableCity State High Low

Phoenix Arizona 105 90

Tuscon Arizona 101 92

Flagstaff Arizona 88 69

San Diego California 77 60

Albuquerque New Mexico 80 60


Database Columns (Fields)

Columns Each column has a name Columns are accessed by name No standard column ordering Does not make sense to say “the third column” like it

does in a “paper” table or spreadsheet Data in a column belongs to a particular domain

Columns are the “attributes” of the dataset Each value in a column is from the same domain Each value in a column is of the same data type


Database Rows (Records)

Rows Each row entry is either a simple value or empty

("null") Rows are sets of values for the columns (attribute

values) Primary key: a set of columns that uniquely

identifies each row Each row must be unique given the primary key (no

duplicates) Rows are referenced by the primary key Row order cannot be determined by the user (Does

not make sense to say “the fourth row” like it does in a “paper” table or spreadsheet)


Data Types Each row value is an instance of a primitive data type

Integer Real (e.g., number, currency Character (e.g., text, hyperlink, yes/no) Date/Time

No complex types in standard DBMS (matrix, drawing) Object oriented databases may allow objects and

structures Non existent value is “null”


Domain types char(n): fixed length char string varchar(n): variable-length char string int or integer smallint numeric(p,d): fixed-point number of given precision real, double precision float(n): floats with a given precision date: containing year,month, and date time: in hours, minutes, and seconds Null value is part of each domain


SQL

Structured Query Language Communicate with databases Used to created and edit databases. Also used to create queries, forms, and

reports


DDL and DML SQL consists of two types of statements

SQL Data Definition Language (DDL) permits database tables to be created or deleted

inserts new data into a database table CREATE TABLE - creates a new database table ALTER TABLE - alters (changes) a database table DROP TABLE - deletes a database table

SQL Data Manipulation Language (DML) SELECT - extracts data from a database table UPDATE - updates data in a database table DELETE - deletes data from a database table INSERT INTO - inserts new data into a database table


Define new domains and tablesCREATE DOMAIN personDom CHAR(20);

CREATE TABLE emp (ename personDom, dno int default 0, sal real);


“Select” clause 1 Specify attributes to project onto

Emp (ename, dno, sal)eName Dno Sal

Jack 111 50K Alice 111 90K Lisa 222 80K Tom 333 70K Mary 333 60K

SELECT *FROM EmpWHERE Emp.Sal < 60K;

use ‘*’ to denote all attributes:

SELECT columns FROM table WHERE condition ;


“Select” clause 2

“SELECT” does not automatically eliminate duplicates.

Emp (ename, dno, sal)eName Dno Sal


Select dnoFrom Emp;

Use keyword distinct to explicitly remove duplicates

Select distinct dnoFrom Emp;


“FROM” clause

Specify relations

E1: Emp (ename, dno, sal)eName Dno Sal


Dept(dno, dname, mgr)dno dname Mgr 111 Sells Alice 222 Toys Lisa 333 Electronics Mary

E2: Emp (ename, dno, sal)eName Dno Sal


SELECT columns FROM table WHERE condition ;

SELECT E1.enameFROM Emp as E1, Dept, Emp as E2WHERE E1.dno = Dept.dno AND Dept.mgr = E2.ename AND E1.sal > E2.sal;

Renaming relations: Use “as” to define “tuple variables,” to disambiguate multiple references to the same relation

?Who makes

more moneythan his boss?


“WHERE” clause Specify optional conditions

“Employees who work for Sally and have a salary < 90K”

SELECT enameFROM Emp, DeptWHERE Emp.dno=Dept.dno AND

D.mgr = ‘Lisa’ AND sal < 90000;

eName Dno Sal Jack 111 50K Alice 111 90K Lisa 222 80K Tom 333 70K Mary 333 60K

dno dname Mgr 111 Sells Alice 222 Toys Lisa 333 Electronics Mary

Emp (ename, dno, sal) Dept(dno, dname, mgr)

Lisa


Conditions Used In Where Clause

= equals

> greater than

< less than

>= greater than or equal to

<= less than or equal to

<> not equal to


Like

Used to make complex searching easy. If you are trying to find all people’s names which begin with E for example:

SELECT firstname FROM employee

WHERE firstname LIKE 'E%';


Ordering output tuplesOrder the tuples by dno. Within each dept, order salaries from highest to lowest. For salary ties, use alphabetical order on the name.

SELECT * FROM Emporder by dno, sal, ename;

ename dno sal location

John 123 10000 NY

Roger 123 12000 NY

Mary 245 69460 London

Susan 323 12300 London

Joe 124 46000 Paris


Set Operations Union: .

Intersect: .

Except: -

(select mgr from D where dname=‘toy’)union(select mgr from D where dname = ‘sells’);

(select mgr from D where dname=‘toy’)intersect(select mgr from D where dname = ‘sales’);

(select mgr from D where dname=‘toy’)except(select mgr from D where dname = ‘sells’);

“Find names of people who are managers of either the toy or the sales department.”

“Find names of people who are managers of both the toy and the sales departments.”

“Find names of people who are managers of the toy but of the sales department.”


Conserving Duplicates The UNION, INTERSECT, and EXCEPT operators use the set

semantics, not bag semantics. To keep duplicates, use “ALL” after the operators:

UNION ALL, INTERSECT ALL, EXCEPT ALL

Student (ssno, name)

Ssno Name 111 Tom 222 Jack 444 Mary

TA (ssno, name)

Ssno Name 111 Tom 222 Jack 555 Alice

111 111 222 222 444 555

Result

(SELECT ssno FROM student)UNION(SELECT ssno FROM ta);

111 222 444 555

ALL


Aggregation functions MIN, MAX, SUM, COUNT, AVG

input: collection of numbers/strings (depending on operation)

output: relation with a single attribute with a single row

“What is the minimum, maximum,

average salary of employees in the toy department”

SELECT MIN(sal), MAX(sal), AVG(sal)FROM Emp, DeptWHERE Emp.dno = Dept.dno and D.dname = ’Toy’;


JOIN

Sometimes we have to select data from two or more tables to make our result complete. We have to perform a join

Tables in a database can be related to each other with keys. A primary key is a column with a unique value for each row. The purpose is to bind data together, across tables, without repeating all of the data in every table.


INNER JOIN

The INNER JOIN returns all rows from both tables where there is a match.

Employee_ID Name

01 Hansen, Ola

02 Svendson, Tove

03Svendson, Stephen

04 Pettersen, Kari

Orders:

Prod_IDProduct Employee_ID

234 Printer 01

657 Table 03

865 Chair 03

Employees:

SELECT Employees.Name, Orders.Product FROM Employees INNER JOIN Orders ON Employees.Employee_ID=Orders.Employee_ID

Result

Name Product

Hansen, Ola Printer

Svendson, Stephen Table

Svendson, Stephen Chair

If there are rows in Employees that do not have matches in Orders, those rows will not be listed


Left\Right Join The LEFT JOIN returns all the rows from the first table (Employees), even if

there are no matches in the second table (Orders).

The RIGHT JOIN returns all the rows from the second table (Orders), even if there are no matches in the first table (Employees).

SELECT Employees.Name, Orders.Product FROM Employees LEFT JOIN Orders ON Employees.Employee_ID=Orders.Employee_ID

SELECT Employees.Name, Orders.Product FROM Employees RIGHT JOIN Orders ON Employees.Employee_ID=Orders.Employee_ID

NameProduct

Hansen, Ola Printer

Svendson, Tove



Pettersen, Kari

Name Product

Hansen, Ola Printer




INSERT INTO

The INSERT INTO statement is used to insert new rows into a table

INSERT INTO table_name VALUES (value1, value2,....)

INSERT INTO table_name (column1, column2,...) VALUES (value1, value2,....)

Or specify the columns for which you want to insert data:


Insert Into Example

LastNameFirstName

Address City

Pettersen Kari Sto 20 Stav

INSERT INTO Persons VALUES ('Hetland', 'Camilla', 'Hagabakka 24', 'Sandnes')

LastNameFirstName

Address City

Pettersen Kari Sto 20 Stav

Hetland Camilla Haga 24 Sandnes


UPDATE

The UPDATE statement is used to modify the data in a table.

UPDATE table_name SET column_name = new_value WHERE column_name = some_value


Person:

LastNameFirstNam

eAddress City

Nilsen Fred Kirk 56 Stav

Rasmussen Sto 67

LastNameFirstName Address City

Nilsen Fred Kirk56 Stav

Rasmussen Nina Sto 67

UPDATE Person

SET FirstName = 'Nina'

WHERE LastName = 'Rasmussen'

UPDATE Person SET Address = 'Stien 12', City = 'Stav' WHERE LastName = 'Rasmussen'



Rasmussen Nina Stien 12 Stav


DELETE The DELETE statement is used to delete

rows in a table.DELETE FROM table_name WHERE column_name = some_value


Nilsen Fred Kirk 56 Stav

DELETE FROM Person WHERE LastName = 'Rasmussen'



Rasmussen Nina Stien 12 Stav


Summary

Why uses databases instead of file systems, what are the pro-cons, when to use each alternative?

What is a relational database? How can you define its semantics?

What is SQL? What are DDL and DML? What statements are related to each SQL rule


Questions?

web programming course, winter 2005 database & sql introduction web programming course...

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