Download PowerPoint - People at SurfaceEffect

Making Database
backed Websites
Session 2
The SQL…
Where do we put the data?
dbwebsites 2.1
How do databases work?
Were going to look at systems known as
Relational Databases.
There are other more modern systems, but
websites almost exclusively use relational systems.
You may hear the terms DBMS and RDBMS,
which stand for Database Management System
and Relational Database Management
System respectively.
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How do databases work?
An DBMS is a server which is responsible for
managing one or more databases.
Database clients can connect to the server to
extract data from the DB or insert data into the
DB.
For a website to use a database it needs a
database client which it can use to extract data
from the database, and use it to generate web
pages. This is built into PHP, which will be covered
in the last session.
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How do databases work?
One DBMS can manage many databases.
Each database contains a number of tables.
Tables have rows of data. Each row is a complete record.
Each column in the table can contain a certain type of data
element, eg numbers, text, dates, etc.
First Name
Char(20)
Surname
Char(20)
Human
Enum(yes,no)
Age
Int
Peter
Mickey
Phone
Char(15)
Email
Char(70)
Bagnall
Yes
29
01524 39145
[email protected]
Mouse
No
74
NULL
[email protected]
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Important Data Types
BOOLEAN
INT(precision)
FLOAT(precision)
DATE, DATETIME, TIMESTAMP[(M)] , TIME, YEAR[(2|4)]
CHAR(M)
VARCHAR(M)
BLOB
TEXT
ENUM('value1','value2',...), SET('value1','value2',...)
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Why Relational?
Data in different tables can be
related
Example:
A person lives at an address.
Several people may live at the
same address.
By joining the people table
and address tables together
you can answer “Where does
X live?” and “Who lives at Y?”.
name
VARCHAR (40)
address
INT(9)
Peter Bagnall
1
Mickey Mouse
2
Goofy
2
address
VARCHAR (200)
id
INT(9)
Castle Park…
1
Disneyland
2
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Schemas
The schema of a database is the design of the
tables, and the way they join together.
Designing the schema for a database is important,
since it can be very hard to change it once a
website is using it without a lot of downtime or
programming effort.
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Schemas - Simplest
Just a single table.
Works for simple lists of records.
First Name
Char(20)
Surname
Char(20)
Human
Enum(yes,no)
Age
Int
Peter
Mickey
Phone
Char(15)
Email
Char(70)
Bagnall
Yes
29
01524 39145
[email protected]
Mouse
No
74
NULL
[email protected]
But people may have home phone, work phone, and mobile phone.
You could add more fields (aka columns) for the extra phone numbers, or…
dbwebsites 2.8
Schemas – One to Many
Can deal with a record of one type relating to several
records of another type.
First Name
Char(20)
Surname
Char(20)
Human
Enum(yes,no)
Age
Int(3)
Peter
Mickey
ID
Int(8)
Email
Char(70)
Bagnall
Yes
29
1
[email protected]
Mouse
No
74
2
[email protected]
Phone Number
Char(15)
Type
Enum(‘home’,’mobile’,’work’,’work fax’)
owner
Int(8)
01524 39145
home
1
07984 168 586
mobile
1
01524 592795
work
1
01524 593608
work fax
1
001 555 956 784
home
2
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Types of Relationships
One to One
Username <-> Password
One to Many
Customer -> Orders
Many to Many
Actors <-> Movies
dbwebsites 2.10
Schemas – Many to Many
Actors
Name
varchar(50)
Michael Caine
Donald Sutherland
DoB
Date
ID
Int(8)
14 March 1933
1
17 July 1935
2
Movies
Title
Varchar(200)
ReleaseDate
Year(4)
ID
Int(8)
The Italian Job
1969
1
Outbreak
1995
2
Get Carter
2000
3
Get Carter
1971
4
Roles
Movie
Int(8)
Actor
Int(8)
Played
Varchar(200)
1
1
Charlie Croker
2
2
Maj. Gen. Donald
McClintock
3
1
Cliff Brumby
4
1
Jack Carter
dbwebsites 2.11
Connect to the DB server
You can access the database interactively through
the windows command line.
mysql -u user -h host –p
User is the username on the database.
Host is the computer which the database is running
on.
Once connected you use SQL to give commands to
the database.
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SQL – Structured Query Language
SQL is the language used to manipulate databases.
mysql> show databases;
+----------+
| Database |
+----------+
| mysql
|
+----------+
1 row in set (0.00 sec)
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Create a database
mysql> create database movies;
Query OK, 1 row affected (0.00 sec)
Now there is a database you can use
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Create some tables
Next you need to create some tables in the
database to hold actual data. First the actors…
mysql> create table actors (name
varchar(50), dob date, id INT(8)
AUTO_INCREMENT primary key);
Query OK, 0 rows affected (0.05 sec)
dbwebsites 2.15
Create more tables
Next the movies…
mysql> create table movies (title
varchar(200), releasedate YEAR, id
INT(8) AUTO_INCREMENT primary key);
Query OK, 0 rows affected (0.03 sec)
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Create last table
Finally the roles, which links the other two tables.
mysql> create table roles (movie
int(8), actor int(8), played
varchar(200));
Query OK, 0 rows affected (0.03 sec)
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Check the tables
You can look at the structure of a table using…
mysql> describe actors;
+-------+-------------+------+-----+---------+----------------+
| Field | Type
| Null | Key | Default | Extra
|
+-------+-------------+------+-----+---------+----------------+
| name | varchar(50) | YES |
| NULL
|
|
| dob
| year(4)
| YES |
| NULL
|
|
| id
| int(8)
|
| PRI | NULL
| auto_increment |
+-------+-------------+------+-----+---------+----------------+
3 rows in set (0.05 sec)
dbwebsites 2.18
Insert some data into the database
Tell it about some actors…
mysql> insert into actors (name, dob)
values (“Michael Caine”,”1935-07-17”);
1 row in set (0.05 sec)
Dates are entered (most easily) in Japanese
format.
The id field is not entered since it is automatically
generated by the database.
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Insert more data into the database
Tell it about some movies…
mysql> insert into movies (title,
releasedate) values (“The Italian
Job”,”1969”);
1 row in set (0.05 sec)
The id field is not entered since it is automatically
generated by the database.
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Which IDs were used?
See what actually went into the database…
mysql> select id, name from actors;
+----+---------------+
| id | name
|
+----+---------------+
| 1 | Michael Caine |
+----+---------------+
1 row in set (0.00 sec)3
mysql> select id, title from movies;
+----+-----------------+
| id | title
|
+----+-----------------+
| 1 | The Italian Job |
+----+-----------------+
1 row in set (0.00 sec)
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Insert more data into the database
Now link the actors to the movies…
mysql> insert into roles (movie,
actor, played) values(1,1,”Charlie
Croker”);
1 row in set (0.05 sec)
The first 1 entered is the id of the movie.
The second 1 is the id of the actor.
dbwebsites 2.22
Answering useful questions
Now that we have a database, with data in it we
can do useful queries. Say we want to know who
played in “The Italian Job”. First find the movie id…
mysql> select id from movies where
title=“The Italian Job”;
+----+
| id |
+----+
| 1 |
+----+
1 row in set (0.00 sec)
dbwebsites 2.23
Answering useful questions
Next link the find any actor id’s which are listed in
the roles as having been in The Italian Job.
mysql> select actor from roles where
movie=1;
+-------+
| actor |
+-------+
|
1 |
+-------+
1 row in set (0.00 sec)
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Answering useful questions
Finally find which actor has the appropriate id.
mysql> select name from actors where
id=1;
+---------------+
| name
|
+---------------+
| Michael Caine |
+---------------+
1 row in set (0.00 sec)
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All in one query!
Or we can combine all those queries into a single
query and have the database do all the work for
us…
mysql> select actors.name from actors,
roles, movies where movies.title =
"The Italian Job" and movies.id =
roles.movie and roles.actor =
actors.id;
+---------------+
| name
|
+---------------+
| Michael Caine |
+---------------+
1 row in set (0.00 sec)
dbwebsites 2.26
Questions?
Presentation online at…
http://people.surfaceeffect.com/pete/
tech/howitworks/dbwebsites/
dbwebsites 2.27