Database Access using SQL
A basic introduction
James Brucker
Database Management System
SELECT * FROM
city WHERE name
LIKE Ban%
Client
User Interface
&
communication
protocol
Database
Manager
Control access to the
database.
• authentication
• enforce permissions
• data integrity
• access services
Database: a structured,
self-describing collection
of data.
Client - Server Databases



Database Server is a separate process on a host.
Clients can be on any machine.
Many programs may be clients using a standard API.
"mysql" utility
Server
mysqld
Java App
+JDBC client
Excel client
Client side
server controls
access to
database
Server side
Install Client Software
For this lab, you will access MySQL server on the
network. All you need is a client application. You don't
need to run a MySQL server on your computer.
Client Tools
mysql-workbench-gpl-5.x.y-win32.msi
or use older GUI Tools:
mysql-gui-tools-5.1.7-win32.msi
From: se.cpe.ku.ac.th/download/mysql
Add MySQL "bin" to your Path
This is so you can run the "mysql" command line.
On Windows:
1. Right-click My Computer.
2. Choose Properties.
3. Click "Advanced".
4. Click "Environment Variables".
5. Edit PATH variable and add:
C:\Windows\blah;C:\Program Files\MySql\bin
Exercise



Use the "mysql" command

if machine doesn't have "mysql" then use MySQL
Query Browser GUI.
What is the client version number?
Use help: how do you connect to a server?
dos> mysql --version
mysql Ver 14.12 Distrib 5.0.16, for Win32
dos> mysql --help
displays a long help message
Exercise

Connect to MySQL server on host "se.cpe.ku.ac.th".


user: student password: student
What MySQL version is the server?
dos> mysql -h se.cpe.ku.ac.th -u student -p
Enter password: nisit
mysql> SELECT version();
Structure of a Database


A database system may contain many databases.
Each database is composed of schema and tables.
sql> SHOW databases;
+--------------+
| Database
|
+--------------+
| mysql
|
| test
|
| bank
|
| world
|
+--------------+
MySQL only shows databases that
a user has permission to access.
sql> USE bank;
sql> SHOW tables;
+----------------+
| Tables_in_bank |
+----------------+
| accounts
|
| clients
|
+----------------+
A Database Structure
Database
Schema
Schema
A database contains schema,
which describe the
organization of the database.
A schema can contain:
Table
Table
Table
Table
field1: t1
field2: t2
field3: t3
field1: t1
field2: t2
field3: t3
field1: t1
field2: t2
field3: t3
field1: t1
field2: t2
field3: t3
indexes
indexes
indexes
indexes
tables - containing data
index files - for fast lookup of
data
stored procedures,
constraints, triggers, and
more
Contents of a Table



A table contains the actual data in records (rows).
A record is composed of fields (columns).
Each record contains one set of data values.
records
(rows)
+------+------------+-------+-------------+---------+
| ID
| Name
| CCode | District
| Populatn
+------+---------------+------------------+---------+
| 3320 | Bangkok
| THA
| Bangkok
| 6320174 |
| 3321 | Nonthaburi | THA
| Nonthaburi | 292100 |
| 3323 | Chiang Mai | THA
| Chiang Mai | 171100 |
+------+------------+-------+-------------+---------+
fields (columns)
Key field for Identifying Rows



A table contains a primary key that uniquely identifies
a row of data.
Each record must have a distinct value of primary key
The primary key is used to relate (join) tables.
ID is the primary key in City table.
+------+------------+-------+-------------+---------+
| ID
| Name
| CCode | District
| Populatn
+------+---------------+------------------+---------+
| 3320 | Bangkok
| THA
| Bangkok
| 6320174 |
| 3321 | Nonthaburi | THA
| Nonthaburi | 292100 |
| 3323 | Chiang Mai | THA
| Chiang Mai | 171100 |
+------+------------+-------+-------------+---------+
Structure of a Table
Every field has:
 a name
 a data type and length
To view the structure of a table use:
DESCRIBE tablename
sql>
DESCRIBE City;
+-------------+-----------+-----+-----+---------+----------------+
| Field
| Type
| Null| Key | Default | Extra
|
+-------------+-----------+-----+-----+---------+----------------+
| ID
| int(11)
| NO | PRI |
| auto_increment |
| Name
| char(35) | NO |
|
|
|
| CountryCode | char(3)
| NO |
|
|
|
| District
| char(20) | NO |
|
|
|
| Population | int(11)
| NO |
| 0
|
|
+-------------+-----------+-----+-----+---------+----------------+
Structure of a Table
"SHOW columns FROM tablename"
shows the same information.
sql>
SHOW columns FROM City;
+-------------+-----------+-----+-----+---------+----------------+
| Field
| Type
| Null| Key | Default | Extra
|
+-------------+-----------+-----+-----+---------+----------------+
| ID
| int(11)
| NO | PRI |
| auto_increment |
| Name
| char(35) | NO |
|
|
|
| CountryCode | char(3)
| NO |
|
|
|
| District
| char(20) | NO |
|
|
|
| Population | int(11)
| NO |
| 0
|
|
+-------------+-----------+-----+-----+---------+----------------+
Fields may have a default
value to use if a value is
not assigned explicitly.
Structured Query Language




Structured Query Language (SQL) is the standard
language for accessing information a database.
SQL is case-insensitive and free format.
Enter commands interactively or in a script file.
SQL statements can use multiple lines

end each statement with a semi-colon ;
sql> USE world;
SQL statements end with semi-colon.
database changed.
sql> SHOW tables;
sql> SHOW columns FROM city;
sql> DECRIBE country;
Exercise
1. Connect to MySQL server on host "se.cpe.ku.ac.th".

user: student password: nisit
2. What databases are on the server?
3. What tables are in the world database?
dos> mysql -h se.cpe.ku.ac.th -u student -p
Enter password: nisit
mysql> SHOW databases;
mysql> USE world;
mysql> SHOW tables;
Exercise
 Omit the semi-colon. What happens?

Enter a command on several lines
mysql> SHOW tables
FROM
world
;
No semi-colon.
DESCRIBE
DESCRIBE shows the structure of a table.

same as "SHOW columns FROM tablename".
sql> DESCRIBE city;
+-------------+-----------+-----+-----+---------+----------------+
| Field
| Type
| Null| Key | Default | Extra
|
+-------------+-----------+-----+-----+---------+----------------+
| ID
| int(11)
| NO | PRI |
| auto_increment |
| Name
| char(35) | NO |
|
|
|
| CountryCode | char(3)
| NO |
|
|
|
| District
| char(20) | NO |
|
|
|
| Population | int(11)
| NO |
| 0
|
|
+-------------+-----------+-----+-----+---------+----------------+
Exercise
For the world database:

what fields does the Country table have?

what information is in the fields?

which fields contain strings? (char or varchar)

which fields contain floating point values?

what is the primary key of the Country table?
Exercise: Case Sensitivity

Is SQL case sensitive?
mysql> DESCRIBE city;
mysql> describe city;

Are names of databases and tables case sensitive?
mysql> use world;
mysql> use WORLD;
mysql> describe city;
mysql> describe City;
Exercise: O-O Analogy of a Table?
Database
table
record (row)
fields (columns)
records
(rows)
Object Oriented
__________________
__________________
__________________
+------+------------+--------------+---------+
| ID
| Name
| District
| Popula..}
+------+------------+--------------+---------+
| 3320 | Bangkok
| Bangkok
| 6320174 |
| 3321 | Nonthaburi | Nonthaburi
| 292100 |
| 3323 | Chiang Mai | Chiang Mai
| 171100 |
+------+------------+--------------+---------+
fields (columns)
Qualifying Names

SQL uses "." to qualify elements of a hierarchy

just like most O-O languages
World.city
"city" table in World db
city.name
name field in city table
World.city.name
fully qualified name
sql> DESCRIBE World.country;
...
sql> SELECT country.name from country;
4 Basic Database Operations
The 4 most common operations:
SELECT
query (search) the data
INSERT
add new records to a table(s)
UPDATE
modify existing record(s)
DELETE
delete record(s) from a table
What is CRUD?
Programmers call these operations "CRUD".
What does CRUD stand for?
Querying Data in a Table
SELECT displays field values from a table:
SELECT field1, field2, field3 FROM table ;

displays ALL rows from the table.

use LIMIT number to limit how many results.
sql> SELECT accountNumber, balance FROM accounts;
+---------------+---------------+----------+---------+
| accountNumber | accountName
| clientID | balance |
+---------------+---------------+----------+---------+
| 11111113
| P.Watanapong | 00001001 | 300000 |
| 11111114
| CPE Fund
| 00001002 | 1840000 |
+---------------+---------------+----------+---------+
SELECT statement with *

Display values for all fields in table:
SELECT * FROM tablename ;
sql> SELECT * from accounts;
+---------------+---------------+----------+---------+
| accountNumber | accountName
| clientID | balance |
+---------------+---------------+----------+---------+
| 11111113
| P.Watanapong | 00001001 | 300000 |
| 11111114
| CPE Fund
| 00001002 | 1840000 |
+---------------+---------------+----------+---------+
Qualifying SELECT

Select columns from a table that match some criteria:
SELECT field1, field2, field3
FROM table
WHERE condition
ORDER BY field1,... [ASC|DESC];
Example: cities with population > 5 M
sql> SELECT * FROM City
WHERE population > 5000000
ORDER BY population DESC;
Strings in SQL

Use single quote mark around String constants.
SELECT * FROM Country
WHERE name = 'Thailand';
SELECT * FROM City
WHERE Name = 'Los Angeles';
Exercises
1. What are the first 3 cities in the database?
2. What are the 3 most populous countries in the world?
3. What is the smallest country in the world? How big?
Exercises for Thailand
1. What is the country code for Thailand?
SELECT * from ... WHERE name = 'Thailand'
2. List the cities in Thailand, sorted by largest population
to smallest. Use "ORDER BY ..."
3. What languages are spoken in Thailand?
4. What countries speak Thai?
WHERE conditions
name = 'Bangkok'
equality test
name LIKE 'Bang%'
pattern match
population >= 100000
population < 500000
gnp <> 0
relations
grade IN
('A','B','C','D','F')
<> is not equals
contained in set
Exercise with WHERE & ORDER
1. What is the most populous country in Europe?

use WHERE continent = ...
2. What countries have name beginning with 'Z'?
3. In Thailand what cities have names like Ban______
Count Function
Select can be used with functions, such as COUNT:
SELECT COUNT(*) FROM accounts
WHERE balance=0;
sql>
SELECT COUNT(*) from accounts;
+----------+
| count(*) |
+----------+
|
4 |
+----------+
sql>
SELECT COUNT(*) from accounts
WHERE balance > 1000000;
Exercise
1. How many countries are in the database?
2. How many cities are in China?
3. How many countries are in Europe?
Other Functions in SQL
Functions can have arguments, just like C, Java, etc.
SUM( expression )
MAX( expression )
MIN( expression )
COUNT( expression )
sql> SELECT MAX(SurfaceArea) FROM country;
1075400.00 (sq.km.)
WRONG: This will NOT find the largest country!
sql> SELECT MAX(SurfaceArea), Name FROM country;
1075400.00
Afghanistan
SELECT functions

How many people are in the world?
SELECT SUM(Population) FROM Country;

How big is the largest country in Asia?
SELECT MAX(SurfaceArea)
FROM Country WHERE continent='Asia';

What is the version of MySQL?
SELECT version();
Exercise
1. What is the total GNP of the entire world?
sql> SELECT sum(GNP) FROM country
1. What are the richest countries (GNP per person) in the
world?
sql> SELECT name, GNP/population
FROM country
ORDER BY GNP/population DESC
LIMIT 20;
 What are the most crowded countries (people per
surface area) in Asia?
Exercise for Functions
Harder:

What are total population and total GNP of each
continent?

Hint: use GROUP BY continent
Expressions and Arithmetic

You can use expressions in SQL.
Arithmetic: + - * / % sqrt()
Grouping: ( )
String ops: substring( ), upper(), length( )
Example: display GNP per person for each country
sql> SELECT name, gnp/population
FROM country
ORDER BY capita_gnp DESC;
AS capita_gnp
Value of GNP is in millions of US Dollars.
How can you show per capita GNP in dollars???
alias
Exercise
1. What countries are the richest? Poorest?

Show the GNP per capita (in US dollars).

Order the results by GNP per capita.
2. What countries are the most crowded?

Crowding refers to population per surface area.
Wildcards to match patterns

Pattern matches: field LIKE 'pattern'
SELECT * FROM city
WHERE name LIKE 'Ban%';
% means "match anything"
Adding New Records

INSERT adds a new record to a table
INSERT INTO table
VALUES ( data1, data2, ...);
sql> INSERT INTO Accounts VALUES
('22222222', 'Ample Rich', '00000001' 10000000);
Query OK, 1 row affected.
+---------------+---------------+----------+---------+
| accountNumber | accountName
| clientID | balance |
+---------------+---------------+----------+---------+
| 22222222
| Ample Rich
| 00000001 |10000000 |
+---------------+---------------+----------+---------+
INSERT into columns by name
INSERT INTO table (field1, field2, ...)
VALUES ( data1, data2, ...);
sql> INSERT INTO Accounts
(accountNumber, balance, accountName)
VALUES
('22222222', 10000000, 'Ample Rich');
Query OK, 1 row affected.
+---------------+---------------+----------+---------+
| accountNumber | accountName
| clientID | balance |
+---------------+---------------+----------+---------+
| 20000000
| Ample Rich
|
|10000000 |
+---------------+---------------+----------+---------+
Exercise

Add your home town to the City table
or, add another city to the City table.
sql> INSERT INTO city
(name, countryCode, district, population)
VALUES
('Bangsaen', 'THA', 'Chonburi', 30000);
Query OK, 1 row affected.
The ID field has a qualifier "AUTO_INCREMENT".
(see: "DESCRIBE City")
This means MySQL will assign the ID value itself.
Exercise

View the City data that you just added!

Correct any errors using UPDATE
sql> SELECT * FROM City
WHERE City.name = 'Bangsaen';
sql> UPDATE City SET population = 33000
WHERE City.name = 'Bangsaen';
Query OK, 1 row affected.
Warning: INSERT is immediate

Change occurs immediately.


unless you are using transactions
Duplicate data is possible.
3 ways to add data to a table
1. INSERT command (boring).
2. Write INSERT commands in a text file and "source"
the file (better).
sql> SOURCE mydata.sql
3. IMPORT command (syntax depends on DBMS):
sql> LOAD DATA INFILE 'filename' INTO table
...
Copying Data Between Tables

Suppose we have another table named NewAccts

NewAccts has accountNumber, accountName, ...
INSERT INTO table (field1, field2, ...)
SELECT field1, field2, field3
FROM other_table
WHERE condition;
sql> INSERT INTO Accounts
SELECT * FROM NewAccounts
WHERE accountNumber NOT NULL;
UPDATE statement
Change values in one or more records:
UPDATE table
SET field1=value1, field2=value2
WHERE condition;
sql> UPDATE city
SET population=40000
WHERE name='Bangsaen' AND countrycode='THA';
Query OK, 1 row affected (0.09 sec)
| name
| countrycode | district | population
|
+----------+-------------+----------+------------------+
| 11111111 | THA
| Chonburi | 40000
|
UPDATE multiple columns
You can change multiple columns:
UPDATE table
SET field1=value1, field2=value2
WHERE condition;
Example: Update population and GNP of Thailand
sql> UPDATE country
SET population=68100000, gnp=345600
WHERE code='THA';
Query OK, 1 row affected (0.09 sec)
Source: CIA World Factbook (on the web)
Warning: don't forget WHERE

UPDATE can change every row in a database

Make sure that your WHERE clause selects
only records you want to change!
sql> UPDATE country
SET population=68100000, gnp=345600 ;
Query OK, 240 rows affected (0.14 sec)
Changed every country
in the database!!
Oops!
I forgot "WHERE ..."
Warning: UPDATE is immediate!

Changes occur immediately. (Can't undo w/o trans.)
Be Careful! If you forget the WHERE clause it will
change all the rows in the table!
sql> UPDATE country SET HeadOfState='Obama';
/* Oops! I forgot "WHERE ..." */
+------+----------------+-------------+--------------+
| Code | Name
| Continent
| HeadOfState |
+------+----------------+-------------+--------------+
| AFG | Afghanistan
| Asia
| Obama
|
| NLD | Netherlands
| Europe
| Obama
|
| ALB | Albania
| Europe
| Obama
|
| DZA | Algeria
| Africa
| Obama
|
| ASM | American Samoa | Oceania
| Obama
|
Obama
rules!
| AND | Andorra
| Europe
| Obama
|
| AGO | Angola
| Africa
| Obama
|
Exercise


Update the City you added to the database.
Change its population.
Deleting Records

DELETE one or more records
DELETE FROM tablename WHERE condition;
Example: Delete all cities with zero population
sql> DELETE FROM City WHERE population <= 0;
Query OK, 5 rows deleted.
Warning: DELETE can delete all

DELETE affects all rows that match.
DELETE FROM tablename WHERE condition;
Example: Delete all cities with zero population
sql> DELETE FROM City
WHERE population <= 0;
Query OK, 5 rows deleted.
Safer Delete

First SELECT the key of the row you want
sql> SELECT id FROM City WHERE name='Bangsaen';
6402

If only one match, then delete using primary key
sql> DELETE FROM City WHERE id=6402;
Relating Tables
The power of a relational database is the
ability to selectively combine data from
many tables.

select data from multiple tables by matching values

Relationship can be:
1-to-1
1-to-many
many-to-1
many-to-many
student -> photograph
country -> city
city -> country
language -> country
Keys
Every table should have a primary key that uniquely
identifies each row.
sql> DESCRIBE Country;
+-------------+-----------+-----+-----+---------+----------------+
| Field
| Type
| Null| Key | Default | Extra
|
+-------------+-----------+-----+-----+---------+----------------+
| Code
| char(3)
| NO | PRI |
|
|
| Name
| char(52) | NO |
|
|
|
| ...
|
|
|
|
|
|
City
ID (PK)
Name
CountryCode (FK)
Population
District
CountryCode
Country
Code (PK)
Name
Continent
Capital
...
Joining Tables

Relate or "join" tables using a condition.

Use "table.field" to qualify a field name:
Country.code
City
ID (PK)
Name
CountryCode (FK)
Population
District
*
Country.name
1
Country
Code (PK)
Name
Continent
Capital
...
City.countrycode = Country.code
Example: Join Country and City
SELECT Country.Name, City.Name
FROM Country, City
WHERE Country.Code = City.CountryCode
AND
Continent = 'South America';
Country
Code
Name
Continent
Region
SurfaceArea
Population
GNP
LocalName
Capital
City
Country.Code = City.CountryCode
ID
Name
CountryCode
District
Population
Use Aliases to Reduce Typing
SELECT co.Name, c.Name
FROM Country co, City c
WHERE co.Code = c.CountryCode
AND
co.Continent = 'South America';
co is alias for Country
c is alias for City
Exercise: Cities in Laos
List the city names and city populations in Laos.
SELECT co.Name, c.Name, c.Population
FROM Country co, City c
WHERE ...
AND
...;
Exercise
1. How can we find the name of the capital city for each
country?
Country
Code (PK)
Name
Continent
Region
SurfaceArea
Population
GNP
LocalName
Capital
City
ID (PK)
Name
CountryCode
District
Population
Exercise Solution
List the country name and capital city name, for all
countries in Asia.
SELECT co.name, c.name AS CapitalCity
FROM Country co, City c
WHERE ...
AND
... ;
Exercise
1. How can we join the CountryLanguage table with the
County table?
Country
Code (PK)
Name
Continent
Region
SurfaceArea
Population
GNP
LocalName
Capital
CountryLanguage
CountryCode
Language
isOfficial
Percentage
FROM Country CO, CountryLanguage L
WHERE ...
Exercise
1. In what countries is the Thai language spoken?
2. By what percentage of the people?
Example:
SELECT CO.name, L.language, L.percentage
FROM Country CO, CountryLanguage L
WHERE ...
AND
... ;
Answer using Aliases

In what countries is Chinese the official language?
SELECT C.name, L.language, L.percentage
FROM Country C, CountryLanguage L
WHERE C.code = L.countrycode
AND L.language LIKE '%Chinese'
AND isOfficial = 'T';
you can omit table name
when there is no ambiguity
alias for
CountryLanguage
Exercise
1. What countries use English?

ORDER the results by percentage spoken, from
largest to smallest %.
2. In how many countries is English the official
language?
Harder
3. In the world, approximately how many people speak
English?

sum( C.population * L.percentage / 100 )
JOIN

Joins tables

Many forms:


INNER JOIN (include only matching columns)

OUTER JOIN (include all columns)

LEFT OUTER JOIN

NATURAL JOIN

CONDITION JOIN
"JOIN" means "INNER JOIN" in MySql.
Example of a Condition Join

JOIN the CountryLanguage and Language tables
using the country code:
SELECT CO.Name, L.language, L.percentage
FROM Country CO
JOIN CountryLanguage L
ON CO.code = L.countrycode
WHERE ...;
Exercise

JOIN the Country and Language tables.

View Country name and language with "SELECT ..."

How many times is Thailand listed in the results?
How can you order the results by language ?
Multiple Table Join

You can join many tables at one time:
SELECT CO.name, C.*, L.language
FROM Country CO
JOIN CountryLanguage L
ON CO.code = L.countrycode
JOIN City C
ON CO.code = C.countrycode
WHERE ...; /* more conditions */
More SELECT Syntax
GROUP BY ...
GROUP BY ... is used when you want to apply a
function (count, sum, avg) to a group of rows having a
common characteristic.
Example: How many countries are in each continent?
SELECT continent, count(*) FROM country
GROUP BY continent
GROUP BY Exercise
What is the total population of each continent?
 use sum(population) and GROUP BY
SELECT continent, SUM(population)
FROM ...
GROUP BY ...
Logical operations

OR
SELECT * FROM City WHERE
District='Songkhla' OR District='Bangkok';

AND
SELECT Name, SurfaceArea FROM Country WHERE
Continent = 'Africa' AND SurfaceArea > 1000000;

NOT
SELECT * FROM Accounts WHERE
NOT AvailableBalance = 0;
Set operations

IN
SELECT * FROM City WHERE
District IN ('Songkhla', 'Bangkok');
Exercise for matching
1. How many countries have a government that is any
form of monarchy?


match any government containing 'Monarchy'
How many are some form of monarchy, but not a
Constitutional Monarchy (like Thailand)?
GROUP BY ... HAVING ...
GROUP BY ... used to apply a function to a group of
rows having a characteristic.
HAVING ... is used to put a condition on the groups.
Example: What countries have more than one official
lanaguage???
SELECT countrycode, count(language)
FROM countrylanguage
???
GROUP BY ... HAVING ...
(1) First, how to count official languages in each country?
SELECT countrycode, count(language)
FROM countrylanguage
WHERE isOfficial='T'
GROUP BY countrycode
GROUP BY ... HAVING ...
(2) add HAVING to restrict results to count( ) > 1
SELECT countrycode, count(language)
FROM countrylanguage
WHERE isOfficial='T'
GROUP BY countrycode
HAVING count(language) > 1
Getting Help
Online help for
 HELP for the mysql command

HELP for SQL statements
mysql> HELP
mysql> HELP SELECT
If MySql doesn't have help on SQL commands, then load the "help
tables" data onto your server. Download help table data from:
http://dev.mysql.com/downloads in the "Documentation" section.
Subqueries

Use the result of one query as part of another query.
Example: Which country has the largest population?
SELECT Name, Population
FROM country
WHERE Population =
( SELECT max(population) FROM country);
Subquery
To use subqueries in MySQL you need version 4.1 or newer.
Exercise


In which country do people live the longest?
How long to they live?
SELECT Name, LifeExpectancy
FROM country
WHERE LifeExpectancy =
( insert subquery here )
;
LIMIT instead of subquery
Another way to get a "most" or "least" result:

ORDER results by what you want. Use ASC or DESC

use LIMIT 1 to limit number of results.
SELECT Name, Population
FROM country
ORDER BY Population DESC
LIMIT 1;
Exercise

Which nation is the most crowded?

Find the country with maximum population density
(population per sq. km.)

Show the name and the population density
Hint: create an alias for a computed field:
sql> SELECT name,
population/surfaceArea AS density
WHERE ...
Alias:
density := population/surfaceArea
Exercise
Is Thailand richer than other countries in Southest Asia?

List the name and GNP/population (=wealth)
of countries in the same region as Thailand.

use a subquery for "the region of Thailand":
SELECT ...
FROM Country
WHERE region = (SELECT region WHERE ...)
ORDER BY ...;
order the results by wealth
Exercise: increasing wealth
Thailand has decided to annex (invade) either Cambodia,
Laus, Vietnam, or Malaysia.
The invaded country will become part of the new Thailand.
The government wants the combined country to be
wealthier than Thailand is now. "wealth" means
GNP/population.
What country should Thailand invade?
Data Definition Commands
These commands alter the structure of a database
CREATE
create a Table, Index, or Database
ALTER
modify structure of a Database or Table
DROP
delete an entire Table, Index, or Database
RENAME
rename a Table
Creating a Table
To add a new table to a database:
CREATE TABLE tablename
(field1, field2, ... )
options ;
sql> CREATE TABLE CUSTOMER (
accountNumber VARCHAR(8) NOT NULL,
clientID
VARCHAR(40) NOT NULL,
balance
DOUBLE DEFAULT '0',
availableBalance DOUBLE DEFAULT '0'
) ;
Query OK, 0 rows affected.
Productivity Hint


Type the "CREATE TABLE" statement into a file.
"source" the file in mysql: source filename;
File: /temp/create-table.sql
CREATE TABLE CUSTOMER (
accountNumber CHAR(10) NOT NULL,
clientID
VARCHAR(40) NOT NULL,
balance
DOUBLE DEFAULT '0',
availableBalance DOUBLE DEFAULT '0',
PRIMARY KEY( clientID )
) ;
sql> SOURCE /temp/create-table.sql;
Query OK, 0 rows affected.
Deleting Records a Table
You must specify a "WHERE" clause for rows to delete.
If there is no "WHERE", it deletes all rows !!
DELETE FROM tablename
WHERE condition ;
-- first use SELECT to verify condition
sql> SELECT * FROM city
WHERE name="Bangsaen";
sql> DELETE FROM city
WHERE name="Bangsaen";
Query OK, 1 row affected.
Exercise

Delete the city you added to the City table.

On a friend's machine, is it deleted immediately?
Deleting a Table
Remove a table from the database
DROP TABLE tablename ;
sql> DROP TABLE CUSTOMER ;
Views

A View is like a "virtual table" containing selected data
from one or more real tables.
Country
Name
Continent
Code
...
CountryLan
guage
Language
Percentage
isOfficial
...
CREATE VIEW MyView AS ...
MyView
Name
Language
Percentage
View Example
Create a view for country name, languages, and
percentage.
sql> CREATE VIEW lang
AS
SELECT name, language, percentage
FROM Country C, CountryLanguage L
WHERE C.code = L.countrycode
ORDER BY language ASC;
Query OK, 0 rows affected.
Use the view to browse data:
sql> SELECT * FROM lang WHERE language='Thai';
Productivity Hint


Type the "CREATE VIEW" statement into a file.
Read the file into mysql: source filename;
File: langview.sql
CREATE VIEW lang AS
SELECT name, language, percentage
FROM Country C, CountryLanguage L
WHERE C.code = L.countrycode;
sql> SOURCE langview.sql;
Query OK, 0 rows affected.
Exercise

Create a view that shows these fields:
City.name as name
Country.name as country
Region
Population of the city
Official language
id of the city

Each person should use a different name for his view,
to avoid interfering with each other.

List the tables in world ( show tables ).
Exercise

List the cities in Southest Asia where English is the
official language and population is over 100,000.
Exercise

Ask MySQL to "describe" your view.

Delete your view:
DROP VIEW viewname ;
Review
What is the command to ...
1. list all the databases that you have access to?
2. use the Bank database?
3. view a list of tables in Bank?
4. view the structure of the Accounts table?
SQL Quiz
Database Game
Vocabulary

"largest" and "smallest" refer to size (surfaceArea).

"most populous", "least populous" refer to population
and population > 0. (exclude unpopulated nations)

"richest", "poorest" means GNP per capita
not total GNP,
and GNP > 0 (GNP = 0 means no data).

"most crowded" refers to population/surfaceArea
Language Hints

"Fortran is an official language" means its an official
language of the country

"Pascal is spoken unofficially" means it is spoken, but
not an official language

"COBOL is spoken" means COBOL is a language
and percentage > 0
What is the World's Smallest Nation?
How big is it?
What is the Largest Country in Africa?


Show the SQL
How big is it?
What are the Poorest Countries in
Asia?

must have GNP data (GNP > 0)

List 3 poorest nations.

What is the GNP per person?
NOTE: GNP is measured in $1,000,000. Multiply your
answer by 1,000,000 to get US$.
What is the Richest Country in the
Middle East (region)?



What is the GNP per person?
Show result is US$ (not million).
Round the income to nearest dollar!

WRONG: 12345.6789
NOTE: GNP is database is measured in $1,000,000.
Multiply your answer by 1,000,000 to get US$.
In what countries is Thai spoken?
SELECT ...
FROM Country C
JOIN CountryLanguage L
ON C.code = L.countrycode
WHERE ...
How many people speak English?
2 queries:
 how many in each country
 total for world
SELECT
FROM
JOIN
ON
WHERE
...
Country C
CountryLanguage L
C.code = L.countrycode
...
History of Empires through Language
Empires are cultures that spread over many countries.
We can detect past Empires by the spread of language.
 What languages are spoken in greatest
number of countries?
 Can you name the Empire?
History of Empires through Language
We can detect past Empires by the spread of language.

What languages are spoken in greatest number of
countries?
SELECT L.language,
sum(L.percentage*C.population) AS sum
FROM Country C
JOIN CountryLanguage L
ON C.code = L.countrycode
GROUP BY L.language
ORDER BY sum DESC
What cities have a population > 6M ?


Print city name, population, and country name
Sort by population -- largest first
+-----------------+------------+-------------------------+
| name
| population | country_name
|
+-----------------+------------+-------------------------+
...
| Bangkok
|
6320174 | Thailand
|
...
Where is Dari the Official Language?
In what country is Dari the official language?
4 official languages?
What country in Europe has 4 official languages?
SELECT
FROM
JOIN
ON
WHERE
GROUP
HAVING
...
Country C
CountryLanguage L
C.code = L.countrycode
...
BY C.code -- group by country
...
Resources
MySQL

http://dev.mysql.com/tech-resources/articles/
Learning SQL

http://www.w3schools.com/sql/
nice tutorial and command reference