Lecture6 MYSQL

8/7/2019 Lecture6 MYSQL

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Hdip Software ProjectMySQL and Database Connectivity through

Java

Dr Martina NaughtonRoom: A1.15

E-mail: [email protected]


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Databases Topics covered this

week

Aims:

MySQL - Intro to the SQL query language

Jdbc connectivity - how to manipulate your

database through Java (JavaBeans/JSPs)


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Part 1: MySQL

About MySQL

Connecting to MySQL

Overview of basic commands

Inserting data

Selecting certain entries

Altering existing entries Deleting data


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Database: recap

A Database is simply a collection of data. In relationaldatabase, data is organized into tables.

Database Management System (DBMS) is software tomaintain and utilize the collections of data (e.g., Oracle,DB2, MySQL)

Students Table

MCCarthyBary3

BloggsJoe2

NaughtonMartina1

last_namefirst_namestudent_id


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About MySQL

MySQL = Free open source SQL (StructuredQuery Language) database server.

SQL language defines how to insert, retrieve,modify and delete data

Your BEST Friend:

MySQL 5.0 ReferenceManual

http://dev.mysql.com/doc/refman/5.0/en/index.html


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Connecting to MySQL

Use mysql on csserver.ucd.ie

Everyone have been granted:

An account on csserver Username = FirstName_initial + Surname

E.g., Martina Naughton = mnaughton

Password = randomly generated (will be handed out after lecture)

A MySQL account Username = same as above

Password = same as above


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Connecting to

csserver.ucd.ie Mac/Linux: open a terminal window and login

using:

ssh [email protected] Windows: download putty connection manager

Download the putty from:http://the.earth.li/~sgtatham/putty/latest/x86/putty.exeand save it on your desktop.

When you double click on putty, you will get thefollowing:


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Putty -- Connection Manager

1. Entercsserver.ucd.ie as the host name 2. Select SSH

3. Click Open


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Start mysql by typing the following command: mysql -u username -p

You give your username with -u, and the -p optiontells MySQL to prompt you for a password.

You will be prompted for your password - Remember: this is the same password as the one you use

to log into yourcsserver.ucd.ie account.

Connecting to MySQL


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If everything is successful, you should see aMySQL command prompt that looks like this:

Connecting to MySQL contd

Welcome to the MySQL monitor. Commands end with ; or \g.

Your MySQL connection id is 688

Server version: 5.0.77-log Source distribution

Type 'help;' or '\h' for help. Type '\c' to clear the

buffer.

mysql>

The version ofMySQL that you are using


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Creating a Database

On csserver.ucd.ie, each user haspermission to create one database. This feature is unique to

csserver(administrators

choice)

All the tables you create will be put in here.

The name of the database MUST be the same asyour username forcsserver.ucd.ie. Again, this feature is unique to csserver


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Creating a Database contd

To create your database, type the following command at theMySQL command prompt:

mysql> CREATE DATABASE database_name;

You can now specify that this is the database that you wantto operate on with this command:

mysql> USE username;

Any other commands you give will now be run on thisdatabase.

NB: Dont forget semi-colons!


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Creating Tables

Inside your database, you will need anumber of tables to hold your data.

Following slide contains a command tocreate tables to hold information aboutstudents.

for this simple example, we're only going tostore their first and last names


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Student Example

mysql> CREATE TABLE students (

student_id INT PRIMARY KEY AUTO_INCREMENT,

first_name VARCHAR(30),

last_name VARCHAR(30)

);


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Student Example contd





);

CREATE TABLE is the name of the command we're trying to run.


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);

Every table must have a primary key - indicated by PRIMARY KEY


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);

AUTO_INCREMENT - useful feature for ids that are numbers

If a student is entered into the database with no id number,

MySQL will automatically give them a student_id that is

one greater than the last student to be put in.


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);

Names of the fields that the table should have


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);





);

The INT datatype indicates that the student_id must be an integer.

VARCHAR(30) says that first_name and last_name are

variable-length strings of characters.

The (30) refers to the maximum length that any first_name or

last_name can be.


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More on creating tables

A database can hold multiple tables

Lets also create another table in the same way, to hold

info about grades

mysql> CREATE TABLE grades (student_id INT,

class_id INT, grade FLOAT, PRIMARY KEY(student_id,

class_id));


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More on creating tables

A database can hold multiple tables

Lets also create another table in the same way,

to hold info about grades

mysql> CREATE TABLE grades (student_id INT,

class_id INT, grade FLOAT, PRIMARY KEY(student_id,

class_id));

NOTE: difference in how primary key is defined here


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Finding out info about your

database Two useful commands

SHOW TABLES command will give you the names ofall the tables that are currently present in your database.

mysql> show tables;+---------------------+

| Tables_in_mnaughton |

+---------------------+

| classes |

| grades |

| students |

+---------------------+

3 rows in set (0.00 sec)


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database contd This command (DESCRIBE) is particularly

important when you want to insert orloaddata into your database.

For these commands, it is necessary to know whatorder the fields should be in.

For the student table above, the first should bestudent_id, followed by first_name andfinally last_name.


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Loading data into your database

Many ways to achieve this

Load from a data file

Insert data one entry/item at a time

This is more than likely what you will be doing

i.e. take data from a webform and enter it into the

database via java program, one item at a time (an

example will follow in later slides)


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Loading from a file

Instead of writing an SQL statement to insert eachitem into your database, you can instead create atab-delimited file.

Each file should have one record per line, with thefields on each line delimited by a tab character.

The fields should be in the same order as they arein your table definition.


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Example File: Students.txt

1 Martina Naughton

2 Tina Woods

3 Bary MCCarthy4 Jeff Phelan

5 Marcus Alvers

6 Michael Amadore

7 Carl Gaffney

8 Rachel Mooney

9 Lisa Fowler

10 AugustMakalakalane

A separates each field


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Loading Data from a file

Use LOAD DATA INFILE command

More info available at:http://dev.mysql.com/doc/refman/5.0/en/load-data.html

Example:mysql> LOAD DATA LOCAL INFILE 'students.txt'INTO TABLE students;

Expected Output:Query OK, 10 rows affected (0.00 sec)

Records: 10 Deleted: 0 Skipped: 0 Warnings: 0


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Entering data one item at a

time Use INSERT command

See http://dev.mysql.com/doc/refman/5.0/en/insert.html for moreinformation

Syntax: INSERT INTO table_name (field_name1,field_name2) VALUES(val1,val2,val3);

Examples:insert into students (student_id, first_name,

last_name) values (1, "Martina", "Naughton");

ORinsert into students (student_id, first_name,

last_name) values (null, joe", Bloggs");

If the field is set to be AUTO_INCREMENT - mysql will assign appropriate value


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Selecting data

Use SELECT statement - possibly the mostcomplex you'll come across

More information available at:http://dev.mysql.com/doc/refman/5.0/en/select.html

This is the command you need to fetch data

from your database.


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By default, the specified rows will be selected from

every row in your table.

Adding a WHERE clause to your statement cancause only particular rows to be selected:mysql> SELECT * FROM students WHERE student_id=2;

+------------+------------+-----------+

| student_id | first_name | last_name |+------------+------------+-----------+


+------------+------------+-----------+

1 row in set (0.00 sec)


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You may get a result list such as:+------------+--------------+

| first_name | last_name |

+------------+--------------+| Martina | Naughton |

| Marcus | Alvers |

| Marcus | Alvers |

| Michael | Amadore |

| Rachel | Mooney |

| August | Makalakalane || August | Makalakalane |

+------------+--------------+

To remove duplicates, use select distinct from instead ofselect from

Duplicates]


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More complex SELECT

queries

For more complex queries, you'll have to

JOIN tables together to get what you're

looking for You'll find the relevant part of the manual here:

http://dev.mysql.com/doc/refman/5.0/en/join.html


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Join Example

Example - to get all the grades relating to aparticular student, you could use the join clause asfollows:mysql> SELECT * FROM students JOIN grades

USING(student_id) WHERE student_id=1;

A couple of points to note on this:

The JOIN we use here causes every row in the studentstable to be linked with every row in the grades table

where the student_id values are the same. The WHERE clause says that we're only interested in

the student with a student_id of 1.


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Join Example contd

Expected output:+------------+------------+-----------+------------+----------+-------+

| student_id | first_name | last_name | student_id | class_id | grade |

+------------+------------+-----------+------------+----------+-------+| 1 | John | Falkner | 1 | 1 | 25.5 |

| 1 | John | Falkner | 1 | 2 | 74.2 |

+------------+------------+-----------+------------+----------+-------+



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Updating Data

Updating data basically means changing

data that's already in the database.

This is done with the UPDATE command

More information available at:http://dev.mysql.com/doc/refman/5.0/en/update.html


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Updating Data contd

For example, we need to change some of thenames of the students in our class. Suppose we'vebeen notified that "Carl Gaffney" spells his name

with a "K".mysql> UPDATE students SET first_name='Karl'WHERE student_id=7;

Multiple fields can be changed at the same time

too. From our data, it looks as if Barry McCarthy'sname was typed in a hurry. To correct it:mysql> UPDATE students SET first_name='Barry',last_name='McCarthy' WHERE student_id=3;


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Updating Data contd

In these examples, we have used the primarykey to identify students that should be

updated, so only one student's information ata time is being changed.

However you should note that any student

that matches the WHERE clause will havetheir data changed.


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Deleting Data

Deletion of data from a table is done with

the DELETE command

More information available at:http://dev.mysql.com/doc/refman/5.0/en/delete.html

For example, to delete a student with the

student id "15", we would use this:

mysql> DELETE FROM students WHERE student_id=15;


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Deleting Data contd

The DELETE command can delete more than one

record at a time, so care is needed. Any record that

matches the WHERE clause will be deleted. Supposing the repeat exams are coming up, so we

want to replace all fail grades with the grade

students got in their repeats. Deleting all grades

under 40% can be done like so:

mysql> DELETE FROM grades WHERE grade


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Deleting Data contd

You can also delete all the data in a table reallyeasy (so be careful!) with the following commands:mysql> DELETE FROM students;

Deletes all entries from students table

mysql> DELETE FROM grades;

Deletes all entries from grades table

mysql> DELETE FROM classes;

Deletes all entries from classes table


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The End for today


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Part 2: Manipulating your databasethrough Java (JavaBeans/JSPs)

Cover on Wednesday..

Lecture6 MYSQL

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