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Database Basics
I101 Summer 2006
Copyright 2004, Matt Hottell
Relational Model
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The relational model is the dominant
model for database design today.
The relational model was conceived by
E.F. Codd of IBM in 1970.
The relational model is based on set
theory and is composed of relations
(also known as tables).
Relations
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Relations are composed of two main
elements:
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Attributes
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Metadata
Tuples
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The data itself
Attributes
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Attributes are the column headings in a
relational table.
They describe the data that is contained
in each column
Order of attributes is unimportant
All of the attributes together make up
the schema of the relation.
Tuples
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Tuples are the complete rows of data in
the table.
They are also known as records.
No two tuples can be exactly the same
The order of tuples is not important
Relation Example
Name
Address
Phone
Matt
420 Baker Street 555-4242
Jenny
12 Tutone Ave
867-5309
Sean
1600 N Penn Dr
555-1550
Relation Example
Attributes
Name
Address
Phone
Matt
420 Baker Street 555-4242
Jenny
12 Tutone Ave
867-5309
Sean
1600 N Penn Dr
555-1550
Relation Example
Tuples
Attributes
Name
Address
Phone
Matt
420 Baker Street 555-4242
Jenny
12 Tutone Ave
867-5309
Sean
1600 N Penn Dr
555-1550
Relation Example
Tuples
Attributes
Schema
Name
Address
Phone
Matt
420 Baker Street 555-4242
Jenny
12 Tutone Ave
867-5309
Sean
1600 N Penn Dr
555-1550
Keys
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Relational tables often have an attribute
or set of attributes that uniquely
identifies each tuple.
These attributes or sets of attributes
are called primary keys.
Example
Name
Address
Phone
Matt
420 Baker Street
555-4242
Jenny
12 Tutone Ave
867-5309
Sean
1600 N Penn Dr
555-1550
Primary Key Example
ID# Name
Address
Phone
500
Matt
420 Baker Street
555-4242
501
Jenny
12 Tutone Ave
867-5309
502
Sean
1600 N Penn Dr
555-1550
Foreign Keys
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Foreign keys are attributes in a
relational table that refer to a primary
key in another relational table.
Foreign keys allow us to link relational
tables together and gather information
based on the contents of multiple
tables.
Foreign Key Example
Cust
ID#
Name
Address
Phone
500
Matt
420 Baker Street
555-4242
501
Jenny
12 Tutone Ave
867-5309
502
Sean
1600 N Penn Dr
555-1550
Trans
ID#
BookID
Date
500
1001
9/13/03
BookID
Title
Price
501
1002
9/17/03
1001
The Code Book
14.00
501
1002
9/26/03
1002
Core Web Programming
49.95
502
1003
10/01/03
1003
The Hacker Ethic
19.95
Book
SQL
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SQL stands for Structured Query
Language.
All Relational Database Management
Systems use SQL to interact with data.
SQL is often implementation-specific
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MySQL uses different syntax than Oracle
We will be using MySQL syntax
Creating a table in SQL
The syntax for creating a table is:
CREATE TABLE tablename
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(column1name datatype(size) [constraints],
column2name datatype(size) [constraints],
column3name datatype(size) [constraints]);
Data Types - Character
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VARCHAR(maxsize)
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variable length character data with a
maximum size of maxsize.
CHAR(fixedsize)
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fixed-length character data of size
fixedsize.
Data Types - Numbers
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INT or INTEGER
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Allocates 4 bytes to store numbers
NUMERIC(precision, scale)
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allocates precision number of digits with
scale decimal places.
Data Types - Dates
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DATE
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TIME
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Stores year, month, day.
Stores hour, minute, second
TIMESTAMP(precision)
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stores year, month, day, hour, minute, and
second.
Constraints
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PRIMARY KEY
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NOT NULL
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Indicates that this attribute is the primary
key for the table
Indicates that this attribute cannot have a
null value
REFERENCES table(attribute)
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Declares that this attribute is a foreign key.
Viewing Relational Tables
SHOW TABLES;
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Displays a list of all the available tables in
the database.
DESCRIBE table_name;
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Displays the schema of the table.
Adding data
You can add data to a table using the
following syntax:
INSERT INTO table_name (attributes)
VALUES (values);
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Character data must be inside single
quotes!
Updating Data
Update the value of a particular
attribute for a tuple:
UPDATE table_name
SET column_name = new_value
WHERE condition to select row to update
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Modifying a table
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Change an attribute’s datatype
ALTER TABLE table_name
MODIFY column_name datatype [NULL| NOT NULL];
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Add an attribute to a table
ALTER TABLE table_name
ADD column_name datatype [NULL | NOT NULL];
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Delete an attribute from a table
ALTER TABLE table_name
DROP COLUMN column_name;
Deleting a table
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DROP TABLE tablename;