Lecture 14 Database.ppt

Introduction to
Database Systems

An overview of last lecture
• Structured Query Language (SQL)
• Manipulating Databases Using SQL

Sequence [TodaysAgenda]
Content of Lecture
• Manipulating Tables Using SQL

Manipulating Tables Using SQL
Select a database
Tables can only exist within a database. Therefore one
needs to select a database first before one can
perform table manipulation. The SQL syntax is:
For example, to select a database named “Amazon”
USE <database_name>;
USE Amazon;

With a database selected, all the table
manipulation using SQL would now occur
within the selected database
Create a table List the tables Examine a table
Alter an existing
table
Delete a table

Create a table
SQL syntax:
CREATE TABLE <table_name>
(
<column_name> <data_type>,
<column_name> <data_type>,
…
<column_name> <data_type>
);
No comma for the
last column
A column name cannot
have any spaces

To store text in a column, choose from the following
data types
Data Type Meaning Example
CHAR(n) If all the data have the same
number of characters, use
CHAR(n)
E.g. Gender CHAR(1)
The data is either 'M' or 'F',
both are 1 character
VARCHAR(n) If all the data have different
number of characters, use
VARCHAR(n)
E.g. LastName VARCHAR(20)
The data cannot have more
than 20 characters
Create a table

To store text in a column, choose from the following
data types
ENUM(valid_text1
, valid_text2…)
Provide a list of allowed
text for a column. Any
text not listed will result
in error
E.g. DepartmentName
ENUM('Information Technology',
'Business', 'Engineering')
Only three valid pieces of text is
allowed: Information Technology,
Business and Engineering
Create a table
Every allowed text needs to
be enclosed in quotes ('')

To store numbers in a column, choose from the
following data types
INT Column can store any integer
from that is between
-2147483648 to 2147483648
E.g. Quantity INT
DECIMAL(m, n) Column can store m digits with
n of the digits being after the
decimal point (.)
E.g. Salary DECIMAL(5, 2)
The input data must be
between -999.99 and 999.99
Create a table

To store numbers in a column, choose from the
INT Column can store any integer
from that is between
-2147483648 to 2147483648
E.g. Quantity INT
DECIMAL(m, n) Column can store m digits with
n of the digits being after the
decimal point (.)
E.g. Salary DECIMAL(5, 2)
The input data must be
between -999.99 and 999.99
Create a table
There are 10 digits:
0, 1, 2, 3, 4, 5, 6, 7, 8, 9

To store date and time in a column, choose from the
DATE Column can store date that is in
the format of ‘year-month-day’
E.g. Birthdate DATE
Data could be '1998-09-04'
DATETIME Column can store both date and
time that is in the format of ‘year-
month-day hour:minute:second’
E.g. Arrival DATETIME
Data could be '2011-11-14
09:41:30'
Create a table

For example, to create a “Book” table with the
following columns
Column Name Data Type
ISBN Integer
Title
Characters (No more than 100
characters)
Quantity Integer
Create a table

The SQL would be as follows
If you execute this SQL, a table named “Book” with 3
columns would be created
CREATE TABLE Book
(
ISBN INT,
Title VARCHAR(100),
Quantity INT
);
Create a table

SQL syntax:
For example, to see a list of all the tables that have
been created within the selected database
List the tables
SHOW TABLES;
SHOW TABLES;

SQL syntax:
DESCRIBE provides information about the columns of
the table including
Column name, data type, whether the column
accepts null or not, is the column a primary
key, etc.
Examine a table
DESCRIBE <table_name>;

For example, to figure out the data type assigned to
each column of the “Book” table
Output of executing the SQL
DESCRIBE Book;
Field Type Null …
ISBN int(11) YES …
Quantity int(11) YES …
Title varchar(100) YES …
Examine a table
Metadata

There are three ways that one can alter an
existing table
Alter an existing table
Altering Table
Add a column
Alter a column
Delete a column

SQL syntax:
For example, to add a column named “NumOfPages”
of type INT to the “Book” table
Add a column
ALTER TABLE <table_name> ADD
<column_name> <data_type>;
ALTER TABLE Book ADD NumOfPages INT;

SQL syntax:
For example, to change the column named “Title” to
“Title1” with data type of VARCHAR(120)
Alter a column
ALTER TABLE <table_name> CHANGE
<column_name> <new_column_name>
<new_data_type>;
ALTER TABLE Book CHANGE Title Title1
VARCHAR(120);

SQL syntax:
For example, to change the data type of “Title” to
VARCHAR(120)
<new_data_type>;
ALTER TABLE Book CHANGE Title Title
VARCHAR(120);
Alter a column

SQL syntax:
For example, to delete the column “NumOfPages”
from the “Book” table
Delete a column
ALTER TABLE <table_name> DROP
<column_name>;
ALTER TABLE Book DROP NumOfPages;

SQL syntax:
For example, to delete the table named “Book”
Delete a table
DROP TABLE <table_name>;
DROP TABLE Book;

Enforcing Data Integrity Using SQL
Since data are stored in tables, MySQL therefore
enforce data integrity (i.e. data correctness) by
allowing restrictions to be placed on the tables
NOT NULL UNIQUE
PRIMARY KEY FOREIGN KEY

NOT NULL
By declaring a column as NOT NULL, this ensures that
the column values cannot be NULL. SQL syntax is:
(
<column_name> <data_type> NOT NULL,
…
);

CREATE TABLE Book
(
ISBN INT,
Title VARCHAR(100) NOT NULL,
Quantity INT
);
For example, to ensure that every book must have a non
NULL “Title”
NOT NULL

To set a column to NOT NULL in an existing table, the
SQL syntax is:
For example, to set the column “Title” to NOT NULL
<new_data_type> NOT NULL;
VARCHAR(100) NOT NULL;
NOT NULL

UNIQUE
By declaring a column as UNIQUE, this ensures that
every column value is different. SQL syntax is:
(
<column_name> <data_type> UNIQUE,
…
);

CREATE TABLE Book
(
ISBN INT,
Title VARCHAR(100) NOT NULL UNIQUE,
Quantity INT
);
For example, to ensure that every book has a non NULL
and unique title
You can have
multiple constraints
per column
UNIQUE

To set a column to UNIQUE in an existing table, the SQL
syntax is:
For example, to set the column “Title” to UNIQUE
<new_data_type> UNIQUE;
VARCHAR(100) UNIQUE;
UNIQUE

Lecture 14 Database.ppt

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