Download PRACTICAL 5

Csc202/csc322 Data Processing and Database Systems
Introduction to MySQL
Aim of this practical
In this practical we are going to familiarise ourselves with MySQL, implement a small
database in MySQL and then perform some simple queries on it. At the end of the practical
you will be able to develop your own database in MySQL.
MySQL
MySQL is a widely used relational database management system, where data is stored in a
series of related tables. MySQL has been developed on the client/server model and written in
C++. MySQL is an interactive program that allows you to connect to a MySQL server, run
queries and view results (it can also be used in batch mode). There is an abundance of
information on the web relating to MySQL. As a starting point please refer to
www.mysql.com and visit the Developer Zone.
The SQL part of MySQL refers to “Structured Query Language” which you will be familiar
with from your lectures and it is the most common language used to access databases.
Getting Started
From the Start menu choose Programs followed by Accessories followed by Command
Prompt. You will have been given a username and a password. At the command prompt
type the following command:
mysql –h csweb2.cs.qub.ac.uk –u your username -p
You will be prompted for a password. Type it in capital letters as it has been given to you.
Once you have the mysql> prompt we recommend that you change your password for
your own security. Type the following:
SET PASSWORD = PASSWORD(‘newpassword’);
And press Return. Try to remember this new password as you will need it the next time
you log on.
Your database name is the same as your username. The final step before you can type your
own SQL statements is to connect to the database. Type the following command
CONNECT database name;
The database
The database we will develop is based on the ER diagram below:
Programmers
Work_on
M
Work
N
Projects
An N:M relationship becomes a separate relation so for the above ER diagram the relational
schema is as follows:
PROGRAMMER (STAFF_NO, NAME, OFFICE_NO, SALARY, JOINING_DATE)
PROJECT (TITLE, START_DATE, DURATION, BUDGET)
WORK_ON (STAFF_NO, TITLE)
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Csc202/csc322 Data Processing and Database Systems
Each relation in the schema will be a table in the database.
Creating a Table
Use the SHOW statement to find out what databases currently exist on the server:
mysql> SHOW DATABASES;
+----------+
| Database |
+----------+
| student1 |
+----------+
The name of the database is probably different on your machine. There are currently
no tables in your database. Type SHOW TABLES; to verify that fact.
In SQL the CREATE TABLE command is used to set up a new table (i.e. to implement a
relation).
For example, to create the table programmer with the attributes staff_no of type integer,
name of type varchar, office_no of type integer, salary of type integer and joining_date of
type date and staff_no as the primary key, type the following command:
CREATE TABLE programmer(staff_no INTEGER, name VARCHAR(20),
office_no INTEGER, salary INTEGER, joining_date DATE, PRIMARY
KEY(staff_no));
When typing a long statement like this one you will have to press return a few times.
This is not a problem as MySQL determines where your statement ends by looking
for the terminating semicolon, not by looking for the end of the input line. (In other
words, MySQL accepts free-format input: it collects input lines but does not execute
them until it sees the semicolon.)
This is what simple multiple-line statement would look like.
mysql> SELECT *
-> FROM programmer;
Now that you have created a table, SHOW TABLES should produce some output:
mysql> SHOW TABLES;
+---------------------+
| Tables_in_student1 |
+---------------------+
| programmer
|
+---------------------+
To verify that your table was created the way you expected, use a DESCRIBE
statement:
mysql> DESCRIBE programmer;
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Csc202/csc322 Data Processing and Database Systems
+--------------+--------------+------+-----+---------+-------+
| Field
| Type
| Null | Key | Default | Extra |
+--------------+--------------+------+-----+-----------------+
| staff_no
| integer
|
| PRI | NULL
| 0
|
| name
| varchar(20) | YES |
| NULL
|
|
| office_no
| integer
| YES |
| NULL
|
|
| salary
| integer
| YES |
| NULL
|
|
| joining_date | date
| YES |
| NULL
|
+--------------+--------------+------+-----+---------+-------+
You can use DESCRIBE any time, for example, if you forget the names of the columns
in your table or what types they have.
Populate your table with data
There are two ways to insert data into a table:
1.
Type the following command to insert one row of data:
INSERT INTO programmer
VALUES (123, ‘Little,Mary’, 12,49000,’1980-6-5’);
note- date format is ‘YYYY-MM-DD’
2.
You can also copy data from a file. Take a copy of the files programmer.txt
and project.txt from S:\library\level2\csc202 into your home directory.
Now type the following command
LOAD DATA LOCAL INFILE 'I:\/path/programmer.txt'
INTO TABLE programmer LINES TERMINATED BY '\r\n';
To look at your table with the data type the following command:
SELECT * FROM PROGRAMMER;
The update command is used to change an existing value. Type the following command:
UPDATE programmer
SET salary = 52000
WHERE name = ‘McIntyre,Jack’;
Use the select command to check that the update has been carried out correctly.
See Appendix 1 for information on using batch files for more efficient processing of your
SQL statements.
See Appendix 2 for information on how to print from MySql.
Create your own table and do some queries.
The data for the project table is in the file project.txt. Create a project table with the
following fields: title of type varchar, start_date of type date, duration of type varchar and
budget of type integer. Use the LOAD DATA LOCAL INFILE command to copy the data
into the project table. Now perform the following queries:
(i)
List everything in the project table.
SELECT * FROM PROJECT;
(ii)
What is the total project budget within the company?
SELECT SUM(budget) FROM PROJECT;
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Csc202/csc322 Data Processing and Database Systems
(iii)
Now here is a query requiring the use of the programmer table. List the names and
office numbers of all pairs of programmers who share an office.
SELECT p1.name, p2.name, p1.office_no
FROM programmer AS p1, programmer AS p2
WHERE p1.office_no = p2.office.no
AND p1.staff_no < p2.staff_no;
(iv)
This query illustrates how you can compare a table to itself. p1 and p2 are both
copies of the programmer table.
Remove all projects with a budget of less than 3000.
DELETE FROM project
WHERE budget < 3000;
List the project table to ensure the deletion has occurred.
Create your own data and corresponding table
As yet the Work_on table does not exist. Use Notepad to create a file with the following
data:
001
003
003
004
Payroll
Newdirectory
Filmstudio
Payroll
(Note: use tabs between each piece of data in a row. Beware of extra blank lines and
spaces. When you have typed the last piece of data, in this case Payroll, press return once.)
Create the table in MySQL and copy the data into it.
(v)
(vi)
List everything in the WORK_ON table.
Finally, retrieve the names of programmers who work on at least one project with a
budget over 4000.
To exit from MySQL type exit at the command prompt.
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Csc202/csc322 Data Processing and Database Systems
Appendix 1
You can run mysql in batch mode. To do this, put the commands you want to run in a file,
then type the following :
mysql> source filename;
There are good reasons for using a script You can generate new queries from existing
ones that are similar by copying and editing script files. If you run a query repeatedly
(say, every day or every week), making it a script allows you to avoid retyping it each
time you execute it.
Appendix 2
In order to print out your results for this practical there are two commands that you need to be
aware of
typing tee filename at the MySQL prompt appends everything that you do
from now on into the file that you have indicated. This file can then be opened in
Notepad, tidied up and then printed.
typing notee at the MySQL prompt will stop the writing to the output file.
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