Mark Dixon Page 1 5 – Persistent data storage: relational databases.

Mark Dixon Page 1

5 – Persistent data storage: relational databases

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Questions: Session variables• Write a line of code to put 31 into a session

variable called score.

• Write code that adds 1 to a variable called g, when a session variable called i is over 25.

if (session.getAttribute("i") > 25){

g = g + 1;

}

Session.setAttribute("score", 31);

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Admin: SQL BookGennick J (2006) SQL Pocket Guide (2nd

edition). O'Reilly.ISBN: 0-596-52688-1

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Session Aims & Objectives• Aims

– To introduce the fundamental ideas involved in using relational databases for persistent data storage

• Objectives,by end of this week’s sessions, you should be able to:

– create a relational database table– create a web page (JSP) that displays data from

a single table in a database– use SQL in your programs to create more

complex record-sets

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Persistent Data Storage• So far

– programs (web-pages) lose data when closed

• Not realistic– typically data stored to persistent storage device

(e.g. hard disk, key drive, floppy disk, CD-RW)

• Use either– flat files– database (relational, or object oriented)

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Example: People (analysis)SPECIFICATION

• User Requirements – need to have access to people's details

• Software Requirements– Functional:

–Display list of people from a database– Non-functional

should be viewable anywhere in the world

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Record Field

Example: People (Database)

ID Surname Forenames Phone Gender

1 Dixon Mark 01752 232556 Male

2 Smith John 01752 111111 Male

3 Jones Sally 01752 888888 Female

• Information organised into– tables (e.g. person)– fields (e.g. phone)– records (e.g. 1 Dixon Mark 01752 232556 …)

Person

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• How many fields?

• How many records?

Questions: Music (Database)

Track Title Artist Name Country

Paranoid Black Sabbath UK

Falling in Love Aerosmith US

Pink Aerosmith US

Love in an Elevator Aerosmith US

Smooth Criminal Alien Ant Farm US

Meaning of Life Disturbed US

The Game Disturbed US

Voices Disturbed US

Down with the Sickness Disturbed US

Track

9

3

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DBMS• Database Management Systems (DBMS)

provide facilities for:– creating and changing databases

• add/remove records• add/remove fields• add/remove data

– For example:• Microsoft Access• dBase• Borland Paradox• MySQL• Microsoft SQL Server• Oracle

home/small business

large scale

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MS Access

Music database

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• Start Menu

• Control Panel

• Administrative Tools

• Data Sources (ODBC)

• System DSN

• Add

How to: Create Data Source64bit Problem – No MS Access driverSolution:use C:\Windows\SysWOW64\odbcad32.exe

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How to: Create Data Source• Select MS Access Driver

• Click Finish

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How to: Create Data Source• Type Data Source Name

• Click Select button

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How to: Create Data Source• Locate Database

• Select Database

• Click OK

• Click OK

• Click OK

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• standard libraryaccess relational databases– establish connection to database– initiating queries – create stored (parameterised) queries – The data structure of query result (table)

• Determining the number of columns• Looking up metadata, etc.

– located in java.sql package

• Note: JDBC not officially an acronym – unofficially “Java Database Connectivity”

JDBC

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Example: People<%@page import="java.sql.*"%><%@page contentType="text/html"%><%Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", "");Statement st = cn.createStatement();ResultSet r = st.executeQuery("SELECT * FROM Person;");String html = ""; while(r.next()){ html += r.getString("Surname"); } cn.close();%><!DOCTYPE html><html> <head><title></title></head> <body> <%=html%> </body></html>

Import JDBC classPeople.jsp

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Example: People 1<%@page import="java.sql.*"%><%@page contentType="text/html"%><%Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", "");Statement st = cn.createStatement();ResultSet r = st.executeQuery("SELECT * FROM Person;");String html = ""; while(r.next()){ html += r.getString("Surname"); } cn.close();%><!DOCTYPE html><html> <head><title></title></head> <body> <%=html%> </body></html>

load driver

People.jsp

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connection

People.jsp

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statement

People.jsp

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results

People.jsp

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process

People.jsp

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closeconnection

People.jsp

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Embedding html in java<%@page import="java.sql.*"%><%@page contentType="text/html"%><%Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", "");Statement st = cn.createStatement();ResultSet r = st.executeQuery("SELECT * FROM Person;");String html = ""; while(r.next()){ html += r.getString("Surname"); } cn.close();%><!DOCTYPE html><html> <head><title></title></head> <body> <%=html%> </body></html>

Need data onseparate lines

html by handput br tags between data 

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Embedding html in java<%@page import="java.sql.*"%><%@page contentType="text/html"%><%Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", "");Statement st = cn.createStatement();ResultSet r = st.executeQuery("SELECT * FROM Person;");String html = ; while(r.next()){ html += r.getString("Surname"); } cn.close();%><!DOCTYPE html><html> <head><title></title></head> <body> <%=html%> </body></html>

error – java does notunderstand html

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Embedding html in java<%@page import="java.sql.*"%><%@page contentType="text/html"%><%Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", "");Statement st = cn.createStatement();ResultSet r = st.executeQuery("SELECT * FROM Person;");String html = " "; while(r.next()){ html += r.getString("Surname"); } cn.close();%><!DOCTYPE html><html> <head><title></title></head> <body> <%=html%> </body></html>

runs, but inwrong place

• Need double quotes around tag

• java sees html as literal string

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Embedding html in java<%@page import="java.sql.*"%><%@page contentType="text/html"%><%Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", "");Statement st = cn.createStatement();ResultSet r = st.executeQuery("SELECT * FROM Person;");String html = ""; while(r.next()){ html += r.getString("Surname"); } cn.close();%><!DOCTYPE html><html> <head><title></title></head> <body> <%=html%> </body></html>

Move br tag inside loop.Which bit of code pulls datafrom database?

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Embedding html in java<%@page import="java.sql.*"%><%@page contentType="text/html"%><%Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", "");Statement st = cn.createStatement();ResultSet r = st.executeQuery("SELECT * FROM Person;");String html = ""; while(r.next()){ html += r.getString("Surname") + " "; } cn.close();%><!DOCTYPE html><html> <head><title></title></head> <body> <%=html%> </body></html>

Move br tag inside loopafter field data

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Embedding html in java• use view source – see what html has been

created:

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Embedding html in java• html must be string (inside double quotes)

• follows normal pattern for expressions:

data

operator

data data data

operator operator

s = s + "" + r.getString("Name") + ""

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Embedding html in java (errors)

s = s + "" r.getString("Gender") + ""

missing operator

s = s + r.getString("Height") + "

missing double quote

s = s + <ul> + r.getString("Height")

html tag must be inside double quotes

s = s + "<ul>" + r.getString("Height")

looks for field in database called Height

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Questions: HTML in java• Are these correct (assume variables and

fields exist)?

g = g + r.getString("Surname ")

h = h + "<ol>" rs.getString("Width")

a = "" + a + ""

html = html + "<img src=face.gif />"

h = <table> + h + "</table>"

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Example: People v2• Display Surname of Male people:

<%@page import="java.sql.*"%><%@page contentType="text/html"%><%Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", "");Statement st = cn.createStatement();ResultSet r = st.executeQuery("SELECT * FROM Person;");String html = ""; while(r.next()){ if (r.getBoolean("Gender")){ html += r.getString("Surname") + " "; } } cn.close();%>

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<%@page import="java.sql.*"%><%@page contentType="text/html"%><%Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", "");Statement st = cn.createStatement();ResultSet r = st.executeQuery("SELECT * FROM Person WHERE Gender = TRUE;");String html = ""; while(r.next()){ html += r.getString("Surname") + " "; } cn.close();%>

Example: People v3• Display Surname of Male people:

SQL statement

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SQL: Queries• main purpose of databases:

– get information back out: searching

• Structured Query Language– dedicated to interacting with databases

• 3rd Generation Language (such as VB, C++)– code describes how to do task

• 4th Generation Language (such as SQL)– code describes what to do (not how to do it)

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SQL: SELECT statement• SELECT statement

– used to get data– can be embedded in VB, via rs.Open:

rs.Open("Person", cs)

rs.Open("SELECT * FROM [Person]", cs)

all fields

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SQL: WHERE & ORDER BY• WHERE clause

– used to restrict data

SELECT * FROM [People] WHERE [age]>=18;

• ORDER BY clause– used to change order of data

SELECT * FROM [People] ORDER BY [Surname];

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SQL: strings (text data)• Possible confusion:

SELECT * FROM Person WHERE Surname = Smith

this will look for field called Smith - gives error need single (SQL) quotes to signify literal text SELECT * FROM Person WHERE Surname = 'Smith'

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SQL & MS access queries• MS Access

– Queries: select data from database– really SQL select statements

– can use queries to test SQL code

MS Access: People.mdb

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Questions: SQL• Create an SQL

statement to extract Track Title of records by Aerosmith




Pink Aerosmith US


Smooth Criminal Alien Ant Farm

US



Voices Disturbed US

Down with the Sickness

Disturbed US

Track

SELECT [Track Title] FROM Track WHERE [Artist Name] = 'Aerosmith';

MS Access: Music.mdb

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Questions: SQL• Create an SQL

statement to extract all fields of songs by Disturbed, ordered by track name




Pink Aerosmith US


Smooth Criminal Alien Ant Farm

US



Voices Disturbed US

Down with the Sickness

Disturbed US

Track

SELECT * FROM Track WHERE [Artist Name] = 'Disturbed' ORDER BY [Track Title];

MS Access: Music.mdb

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Example: People v4

• User controls what is displayed:

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SQL: DISTINCT records

SELECT [Artist Name]FROM [Track];

Artist Name

Black Sabbath

Aerosmith

Aerosmith

Aerosmith

Alien Ant Farm

Disturbed

Disturbed

Disturbed

Disturbed

Artist Name

Black Sabbath

Aerosmith

Alien Ant Farm

Disturbed

SELECT DISTINCT [Artist Name]FROM [Track];

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Tutorial Exercise: People• Task 1: Create your own People database:

– Open MS Access– Create a new database file– Create a new table– Create fields– Enter data

• Task 2: Get the People v1 example (from the lecture) working.• Task 3: Modify your page so that it displays phone number as well as the

person's name.• Task 4: Modify your page so that it displays the data in an html table.• Task 5: Modify your page so that records for males are displayed in blue, and

records for females are displayed in red.• Task 6: Modify your page as per version 4. You will need to:

– Add a form to the page, and three submit buttons– In your code, detect when a button has been pressed (have a look at

previous weeks)• Task 7: Modify your page so that the user can type a letter, and only names

starting with that letter are displayed.• Task 8: Modify your page so that the user can type a series of numerical digits

and only phone numbers containing those digits are displayed.• Task 9: Modify your code so that the user can order the data by surname, or

email address (You may want to use a Query String)

Mark Dixon Page 1 5 – Persistent data storage: relational databases.

Documents

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