Database Management Systems MySQL – Lab Exercises

Exercise - 1

RDBMS stands for Relational Database Management System.

RDBMS is the basis for SQL, and for all modern database systems such as MS SQL Server, IBM DB2, Oracle,
MySQL, and Microsoft Access.

The data in RDBMS is stored in database objects called tables.

A table is a collection of related data entries and it consists of columns and rows.

SQL is a standard language for accessing and manipulating databases.

What is SQL?
 SQL stands for Structured Query Language
 SQL lets you access and manipulate databases
 SQL is an ANSI (American National Standards Institute) standard

What Can SQL do?

 SQL can execute queries against a database
 SQL can retrieve data from a database
 SQL can insert records in a database
 SQL can update records in a database
 SQL can delete records from a database
 SQL can create new databases
 SQL can create new tables in a database
 SQL can create stored procedures in a database
 SQL can create views in a database
 SQL can set permissions on tables, procedures, and views

Although SQL is an ANSI (American National Standards Institute) standard, there are many different
versions of the SQL language.

However, to be compliant with the ANSI standard, they all support at least the major commands
(such as SELECT, UPDATE, DELETE, INSERT, WHERE) in a similar manner.

MySQL Data Types

In MySQL there are three main types : text, number, and Date/Time types.

Text types:

Data type Description

CHAR(size) Holds a fixed length string (can contain letters, numbers, and special characters).
The fixed size is specified in parenthesis. Can store up to 255 characters
VARCHAR(size) Holds a variable length string (can contain letters, numbers, and special
characters). The maximum size is specified in parenthesis. Can store up to 255
characters. Note: If you put a greater value than 255 it will be converted to a
TEXT type
TINYTEXT Holds a string with a maximum length of 255 characters
TEXT Holds a string with a maximum length of 65,535 characters
BLOB For BLOBs (Binary Large OBjects). Holds up to 65,535 bytes of data
MEDIUMTEXT Holds a string with a maximum length of 16,777,215 characters

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MEDIUMBLOB For BLOBs (Binary Large OBjects). Holds up to 16,777,215 bytes of data
LONGTEXT Holds a string with a maximum length of 4,294,967,295 characters
LONGBLOB For BLOBs (Binary Large OBjects). Holds up to 4,294,967,295 bytes of data
ENUM(x,y,z,etc.) Let you enter a list of possible values. You can list up to 65535 values in an ENUM
list. If a value is inserted that is not in the list, a blank value will be inserted.

Note: The values are sorted in the order you enter them.

You enter the possible values in this format: ENUM('X','Y','Z')

SET Similar to ENUM except that SET may contain up to 64 list items and can store
more than one choice

Number types:

Data type Description

TINYINT(size) -128 to 127 normal. 0 to 255 UNSIGNED*. The maximum number of digits may
be specified in parenthesis
SMALLINT(size) -32768 to 32767 normal. 0 to 65535 UNSIGNED*. The maximum number of digits
may be specified in parenthesis
MEDIUMINT(size) -8388608 to 8388607 normal. 0 to 16777215 UNSIGNED*. The maximum
number of digits may be specified in parenthesis
INT(size) -2147483648 to 2147483647 normal. 0 to 4294967295 UNSIGNED*. The
maximum number of digits may be specified in parenthesis
BIGINT(size) -9223372036854775808 to 9223372036854775807 normal. 0 to
18446744073709551615 UNSIGNED*. The maximum number of digits may be
specified in parenthesis
FLOAT(size,d) A small number with a floating decimal point. The maximum number of digits may
be specified in the size parameter. The maximum number of digits to the right of
the decimal point is specified in the d parameter
DOUBLE(size,d) A large number with a floating decimal point. The maximum number of digits may
be specified in the size parameter. The maximum number of digits to the right of
the decimal point is specified in the d parameter
DECIMAL(size,d) A DOUBLE stored as a string , allowing for a fixed decimal point. The maximum
number of digits may be specified in the size parameter. The maximum number of
digits to the right of the decimal point is specified in the d parameter

*The integer types have an extra option called UNSIGNED. Normally, the integer goes from an negative to
positive value. Adding the UNSIGNED attribute will move that range up so it starts at zero instead of a
negative number.

Date types:

Data type Description

DATE() A date. Format: YYYY-MM-DD

Note: The supported range is from '1000-01-01' to '9999-12-31'

DATETIME() *A date and time combination. Format: YYYY-MM-DD HH:MM:SS

Note: The supported range is from '1000-01-01 00:00:00' to '9999-12-31

23:59:59'
TIMESTAMP() *A timestamp. TIMESTAMP values are stored as the number of seconds since the
Unix epoch ('1970-01-01 00:00:00' UTC). Format: YYYY-MM-DD HH:MM:SS

Note: The supported range is from '1970-01-01 00:00:01' UTC to '2038-01-09

03:14:07' UTC
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Database Management Systems MySQL – Lab Exercises
TIME() A time. Format: HH:MM:SS

Note: The supported range is from '-838:59:59' to '838:59:59'

YEAR() A year in two-digit or four-digit format.

Note: Values allowed in four-digit format: 1901 to 2155. Values allowed in two-
digit format: 70 to 69, representing years from 1970 to 2069

*Even if DATETIME and TIMESTAMP return the same format, they work very differently. In an INSERT or
UPDATE query, the TIMESTAMP automatically set itself to the current date and time. TIMESTAMP also accepts
various formats, like YYYYMMDDHHMMSS, YYMMDDHHMMSS, YYYYMMDD, or YYMMDD.

Database Tables
A database most often contains one or more tables. Each table is identified by a name (e.g. "Customers" or
"Orders"). Tables contain records (rows) with data.

Below is an example of a table called "Persons":

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger

The table above contains three records (one for each person) and five columns (P_Id, LastName, FirstName,
Address, and City).

SQL Statements
Most of the actions you need to perform on a database are done with SQL statements.

The following SQL statement will select all the records in the "Persons" table:

SELECT * FROM Persons

 SQL is not case sensitive

Semicolon after SQL Statements?

Some database systems require a semicolon at the end of each SQL statement.

Semicolon is the standard way to separate each SQL statement in database systems that allow more than one
SQL statement to be executed in the same call to the server.

We are using MS Access and SQL Server 2000 and we do not have to put a semicolon after each SQL
statement, but some database programs force you to use it.

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SQL DML and DDL

SQL can be divided into two parts: The Data Manipulation Language (DML) and the Data Definition Language
(DDL).

The query and update commands form the DML part of SQL:

 SELECT - extracts data from a database

 UPDATE - updates data in a database
 DELETE - deletes data from a database
 INSERT INTO - inserts new data into a database

The DDL part of SQL permits database tables to be created or deleted. It also defines indexes (keys), specifies
links between tables, and imposes constraints between tables. The most important DDL statements in SQL
are:

 CREATE DATABASE - creates a new database

 ALTER DATABASE - modifies a database
 CREATE TABLE - creates a new table
 ALTER TABLE - modifies a table
 DROP TABLE - deletes a table
 CREATE INDEX - creates an index (search key)
 DROP INDEX - deletes an index

The SQL SELECT Statement

The SELECT statement is used to select data from a database.

The result is stored in a result table, called the result-set.

SQL SELECT Syntax

SELECT column_name(s)
FROM table_name

and

SELECT * FROM table_name

The SQL SELECT Statement

The SELECT statement is used to select data from a database.

The result is stored in a result table, called the result-set.

SQL SELECT Syntax

SELECT column_name(s)
FROM table_name

and

SELECT * FROM table_name

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Note: SQL is not case sensitive. SELECT is the same as select.

An SQL SELECT Example

The "Persons" table:

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes

2 Svendson Tove Borgvn 23 Sandnes

3 Pettersen Kari Storgt 20 Stavanger

Now we want to select the content of the columns named "LastName" and "FirstName" from the table above.

We use the following SELECT statement:

SELECT LastName,FirstName FROM Persons

The result-set will look like this:

LastName FirstName

Hansen Ola

Svendson Tove

Pettersen Kari

SELECT * Example
Now we want to select all the columns from the "Persons" table.

We use the following SELECT statement:

SELECT * FROM Persons

Tip: The asterisk (*) is a quick way of selecting all columns!

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The result-set will look like this:

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes

2 Svendson Tove Borgvn 23 Sandnes

3 Pettersen Kari Storgt 20 Stavanger

The SQL SELECT DISTINCT Statement

In a table, some of the columns may contain duplicate values. This is not a problem, however, sometimes you
will want to list only the different (distinct) values in a table.

The DISTINCT keyword can be used to return only distinct (different) values.

SQL SELECT DISTINCT Syntax

SELECT DISTINCT column_name(s)
FROM table_name

SELECT DISTINCT Example

The "Persons" table:

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes

2 Svendson Tove Borgvn 23 Sandnes

3 Pettersen Kari Storgt 20 Stavanger

Now we want to select only the distinct values from the column named "City" from the table above.

We use the following SELECT statement:

SELECT DISTINCT City FROM Persons

The result-set will look like this:

City

Sandnes

Stavanger

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The WHERE Clause

The WHERE clause is used to extract only those records that fulfill a specified criterion.

SQL WHERE Syntax

SELECT column_name(s)
FROM table_name
WHERE column_name operator value

WHERE Clause Example

The "Persons" table:

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes

2 Svendson Tove Borgvn 23 Sandnes

3 Pettersen Kari Storgt 20 Stavanger

Now we want to select only the persons living in the city "Sandnes" from the table above.

We use the following SELECT statement:

SELECT * FROM Persons

WHERE City='Sandnes'

The result-set will look like this:

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes

2 Svendson Tove Borgvn 23 Sandnes

Quotes Around Text Fields

SQL uses single quotes around text values (most database systems will also accept double quotes).

However, numeric values should not be enclosed in quotes.

For text values:

This is correct:

SELECT * FROM Persons WHERE FirstName='Tove'

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This is wrong:

SELECT * FROM Persons WHERE FirstName=Tove

For numeric values:

This is correct:

SELECT * FROM Persons WHERE Year=1965

This is wrong:

SELECT * FROM Persons WHERE Year='1965'

Operators Allowed in the WHERE Clause

With the WHERE clause, the following operators can be used:

Operator Description

= Equal

<> Not equal

> Greater than

< Less than

>= Greater than or equal

<= Less than or equal

BETWEEN Between an inclusive range

LIKE Search for a pattern

IN To specify multiple possible values for a column

The AND & OR Operators

The AND operator displays a record if both the first condition and the second condition are true.

The OR operator displays a record if either the first condition or the second condition is true.

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AND Operator Example
The "Persons" table:

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger

Now we want to select only the persons with the first name equal to "Tove" AND the last name equal to
"Svendson":

We use the following SELECT statement:

SELECT * FROM Persons

WHERE FirstName='Tove'
AND LastName='Svendson'

The result-set will look like this:

P_Id LastName FirstName Address City

2 Svendson Tove Borgvn 23 Sandnes

OR Operator Example
Now we want to select only the persons with the first name equal to "Tove" OR the first name equal to "Ola":

We use the following SELECT statement:

SELECT * FROM Persons

WHERE FirstName='Tove'
OR FirstName='Ola'

The result-set will look like this:

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes

Combining AND & OR

You can also combine AND and OR (use parenthesis to form complex expressions).

Now we want to select only the persons with the last name equal to "Svendson" AND the first name equal to
"Tove" OR to "Ola":

We use the following SELECT statement:

SELECT * FROM Persons WHERE

LastName='Svendson'
AND (FirstName='Tove' OR FirstName='Ola')
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Database Management Systems MySQL – Lab Exercises
The result-set will look like this:

P_Id LastName FirstName Address City

2 Svendson Tove Borgvn 23 Sandnes

The ORDER BY keyword is used to sort the result-set.

The ORDER BY Keyword

The ORDER BY keyword is used to sort the result-set by a specified column.

The ORDER BY keyword sorts the records in ascending order by default.

If you want to sort the records in a descending order, you can use the DESC keyword.

SQL ORDER BY Syntax

SELECT column_name(s) FROM table_name ORDER BY column_name(s) ASC|DESC

ORDER BY Example
The "Persons" table:

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes

2 Svendson Tove Borgvn 23 Sandnes

3 Pettersen Kari Storgt 20 Stavanger

4 Nilsen Tom Vingvn 23 Stavanger

Now we want to select all the persons from the table above, however, we want to sort the persons by their
last name.

We use the following SELECT statement:

SELECT * FROM Persons ORDER BY LastName

The result-set will look like this:

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes

4 Nilsen Tom Vingvn 23 Stavanger

3 Pettersen Kari Storgt 20 Stavanger

2 Svendson Tove Borgvn 23 Sandnes

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ORDER BY DESC Example

Now we want to select all the persons from the table above, however, we want to sort the persons descending
by their last name.

We use the following SELECT statement:

SELECT * FROM Persons

ORDER BY LastName DESC

The result-set will look like this:

P_Id LastName FirstName Address City

2 Svendson Tove Borgvn 23 Sandnes

3 Pettersen Kari Storgt 20 Stavanger

4 Nilsen Tom Vingvn 23 Stavanger

1 Hansen Ola Timoteivn 10 Sandnes

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