Database Access using SQL Very basic introduction James Brucker.

Database Access using SQL

Very basic introduction

James Brucker

Database Management System

Database: a structured, self-describing collection of data.

controls access to the database & provides:• authentication• enforce permissions• data integrity• access services

Database Manager

User Interface & communications protocol

SELECT * FROM city WHERE name LIKE Ban%

User

Client - Server Structure

The database server is a separate process running on a host.

The database client can be on a different machine. Many programs may be client using standard API.

mysqld(server)client using "mysql" utility

client using Java+JDBC

client using Excel

Exercise

Use the "mysql" command if machine doesn't have "mysql" then use MySQL

Query Browser GUI. What is the version number? Look at help message: how do you connect to server?

dos> mysql --version

mysql Ver 14.12 Distrib 5.0.16, for Win32

dos> mysql --help

displays a long help message: very useful

Exercise

Connect to MySQL server on host "se.cpe.ku.ac.th".

user: student password: student

What MySQL version is the server running?

dos> mysql -h se.cpe.ku.ac.th -u student -p

Enter password: student

mysql> SELECT version();

mysql>

Structure of a Database

A database system may contain many databases. Each database is composed of schema and tables.

sql> USE bank;

sql> SHOW tables;+----------------+| Tables_in_bank |+----------------+| accounts || clients |+----------------+

sql> SHOW databases;+--------------+

| Database |

+--------------+

| mysql |

| test |

| bank |

| world |

+--------------+

MySQL only shows databases that a user has permission to access.

Structured Query Language

The standard language for manipulating a database is Structured Query Language (SQL).

SQL is case-insensitive and free format. Commands are entered interactively or in a script file. SQL statements can span multiple lines:

end a statement with a semi-colon ;

sql> USE Bank;

database changed.

sql> SHOW tables;

sql> SHOW columns FROM accounts;

sql> SELECT accountNumber, accountName,

clientID, balance FROM accounts;

SQL statements end with a semi-colon.

A Simple Database Structure

SQL commands to show the structure of Bank database

sql> SHOW tables;+----------------+| Tables_in_bank |+----------------+| accounts || clients |+----------------+

sql> SHOW columns FROM accounts;+------------------+-------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+------------------+-------------+------+-----+---------+-------+| accountNumber | varchar(8) | | | | || accountName | varchar(40) | | | | || clientID | int(11) | | MUL | 0 | || balance | double | | | 0 | || availableBalance | double | | | 0 | |+------------------+-------------+------+-----+---------+-------+

SQL statements must end with a semi-colon. If you omit semi-colon, SQL will prompt for more input.

Exercise

Connect to MySQL server on host "se.cpe.ku.ac.th".

user: student password: student

What databases are there?

What tables are in the world database?

dos> mysql -h se.cpe.ku.ac.th -u student -p

Enter password: student

mysql> SHOW databases;

mysql> SHOW tables from world;

mysql> USE world;

mysql> SHOW tables;

Exercise

Omit the semi-colon. What happens?

mysql> SHOW tablesNo semi-colon.

Enter a command on several lines

mysql> SHOW

tables

from

world

;

Structure of a Database Table

A table contains records (rows) of data. A record is composed of several columns (fields). A database schema can contain index files, views,

and other information in addition to tables.

sql> SELECT * FROM Accounts;+---------------+---------------+----------+---------+

| accountNumber | accountName | clientID | balance |

+---------------+---------------+----------+---------+

| 11111111 | J.Brucker | 11111111 | 35000 |

| 11111112 | Vacation Fund | 11111111 | 22500 |

| 11111113 | P.Watanapong | 11111120 | 300000 |

| 11111114 | CPE Fund | 11111120 | 1840000 |

+---------------+---------------+----------+---------+

DESCRIBE

DESCRIBE also shows a description of a table. output is same as "SHOW COLUMNS FROM ...".

sql> DESCRIBE accounts;+------------------+-------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+------------------+-------------+------+-----+---------+-------+| accountNumber | varchar(8) | | | | || accountName | varchar(40) | | | | || clientID | int(11) | | MUL | 0 | || balance | double | | | 0 | || availableBalance | double | | | 0 | |+------------------+-------------+------+-----+---------+-------+

Exercise:

For the world database:

what columns does each table have?

what information do you suppose is in the columns?

What are the names of some data types in SQL?

mysql> describe city;+-------------+----------+------+-----+---------+-----------+| Field | Type | Null | Key | Default | Extra |+-------------+----------+------+-----+---------+-----------+| ID | int(11) | NO | PRI | NULL | auto_incr || Name | char(35) | NO | | | || CountryCode | char(3) | NO | | | || District | char(20) | NO | | | || Population | int(11) | NO | | 0 | |+-------------+----------+------+-----+---------+-----------+

Exercise: O-O Analogy of a Table?

Database Object Oriented

table __________________

record (row) __________________

fields (columns) __________________

sql> SELECT * FROM Accounts;+---------------+---------------+----------+---------+


+---------------+---------------+----------+---------+

| 11111111 | J.Brucker | 11111111 | 35000 |

| 11111112 | Vacation Fund | 11111111 | 22500 |

| 11111113 | P.Watanapong | 11111120 | 300000 |

| 11111114 | CPE Fund | 11111120 | 1840000 |

+---------------+---------------+----------+---------+

Qualifying Names

SQL uses "." to qualify elements of a hierarchy just like most O-O languages

Bank.accounts "accounts" table in Bank db

accounts.balance balance field in accounts

Bank.accounts.balance

sql> DESCRIBE bank.accounts;+------------------+-------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+------------------+-------------+------+-----+---------+-------+| accountNumber | varchar(8) | | | | || accountName | varchar(40) | | | | || clientID | int(11) | | MUL | 0 | || balance | double | | | 0 | || availableBalance | double | | | 0 | |+------------------+-------------+------+-----+---------+-------+

Diagram of Database Structure

Database

Catalog

Schema

Tablefield1: t1field2: t2field3: t3

indexes

Schema


indexes


indexes


indexes

Catalog

Schema


indexes

Schema


indexes


indexes


indexes

In MySQL the words "database" and "schema" are used inconsistently.

Database Operations

Operations you can perform on a database include:

USE choose a database

SELECT query (search) the data

INSERT add new records to a table(s)

UPDATE modify information in existing records

DELETE delete records from a table

sql> USE bank;sql> SELECT * FROM clients WHERE firstname = 'james';| clientID | firstName | lastName | email |+----------+-----------+----------+--------------------+| 11111111 | James | Brucker | [email protected] |sql> UPDATE accounts SET balance=100000 WHERE clientID='11111111';Query OK, 1 row affected (0.09 sec)

SQL SELECT statement

Select columns from a table and display them:

SELECT field1, field2, field3 FROM tablename ;

This displays ALL rows from the table.

sql> SELECT * from accounts;+---------------+---------------+----------+---------+


+---------------+---------------+----------+---------+

| 11111111 | J.Brucker | 11111111 | 35000 |

| 11111112 | Vacation Fund | 11111111 | 22500 |

| 11111113 | P.Watanapong | 11111120 | 300000 |

| 11111114 | CPE Fund | 11111120 | 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];

SQL statements and field names are case insensitive, but the field values may not be! It depends on the data type of the field.

sql> SELECT accountNumber, ... FROM accounts WHERE balance > 100000 ORDER by balance DESC;+---------------+---------------+----------+---------+


+---------------+---------------+----------+---------+

| 11111114 | CPE Fund | 11111120 | 1840000 |

| 11111113 | P.Watanapong | 11111120 | 300000 |

+---------------+---------------+----------+---------+

Counting with SELECT

Select can be used with functions, such as COUNT:

SELECT COUNT(*) from Accounts WHERE condition;

sql> SELECT count(*) from accounts;+----------+

| count(*) |

+----------+

| 4 |

+----------+

sql> SELECT count(*) from accounts

WHERE balance > 100000;

Exercise:

Use the world database to answer these questions: How many countries and cities are in the database?

What is the country code for China?

use the condition WHERE name = 'China'

How many cities are in China?

What languages are spoken in China?

what is the official language?

List the cities in China, sorted by population (largest to smallest). Use "ORDER BY ..."

Exercise:

What is the country code for Thailand?

What is the population of Thailand?

How many cities are in Thailand?

what are the names of the cities?

What languages are used in Thailand?

Strings and wildcards in SELECT

Use single quote marks for String data. For exact matches use field = 'value'

SELECT * FROM city

WHERE CountryCode = 'THA';

For pattern matches, use: field LIKE 'pattern'

SELECT * FROM city WHERE name LIKE 'Ba%';

In SQL, '%' means "match anything".

SELECT * FROM clients WHERE firstName LIKE 'J%' ORDER BY lastName;

SQL statements and field names are case insensitive, but the field values may not be! It depends on the data type of the field.

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: who lives longest?

How many countries are in Asia?

In which countries in Asia do people live longest?

List the countries sorted by life expectancy.

Where can you expect to live > 80 years?

What country in Asia has the shortest life expectancy?

How does Thailand rank for life expectancy?

COUNT the countries in Asia with life expectancy less than in Thailand.

COUNT the countries in Asia with life expectancy greater than in Thailand.

Exercise

Find all cities in Thailand, ranked by Population

use: "SELECT ... ORDER BY Population DESC"

do you see any errors in the data?

Using Functions in SELECT

How many people are in the world?

SELECT SUM(population) FROM Country;

What is the largest surface area of any country?

SELECT MAX(SurfaceArea) FROM Country;

How many cities are from Thailand?

SELECT COUNT(*) FROM CityWHERE countrycode = 'THA';

What is the version of MySQL?

SELECT version();

Exercise

What is the total population of the world?

What is the total population of Asia?

What is the average and maximum population per sq.km. of the countries in the world?

Country.SurfaceArea is the area in sq. km.

Getting Help

Built-in help for how to use the mysql command SQL statements

mysql> HELP

mysql> HELP SELECT

If mysql doesn't have help on SQL commands, then load the "help tables" data onto the server. Download help table data from:

http://dev.mysql.com/downloads in the "Documentation" section.

Using Subqueries

Use the result of one query as part of another query.

Which account has the greatest balance?

SELECT AccountNumber, AccountNameFROM AccountsWHERE balance =

( SELECT max(balance) FROM Accounts );

Where do people live the longest?

SELECT Name, LifeExpectancy FROM CountryWHERE LifeExpectancy =( SELECT max(LifeExpectancy) FROM Country );

To use SQL subqueries in MySQL you need version 4.1 or newer.

Exercise

Where do people live longer than in Thailand?

ORDER the results by DESCending life expectancy.

SELECT Name, LifeExpectancy FROM CountryWHERE LifeExpectancy >

( insert subquery here )

ORDER BY ... ;

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 densityWHERE ...

Alias:density := population/surfaceArea

Exercise

Is Thailand more crowded than neighbor countries?

List the name and population density of all countries in the same region as Thailand.

use a subquery for "same region as Thailand":

SELECT ... FROM Country

WHERE Region = (SELECT Region ... Code=...) ORDER ...;

Order the results by population density.

Exercise

How does Thailand's economic output per capita compare with other countries in Asia?

Compare 1,000,000 * GNP / population.

Modify data with UPDATE

UPDATE changes data in one or more tables:

UPDATE accounts SET balance=100000 WHERE clientID='11111111';

sql> UPDATE accounts SET balance=100000 WHERE clientID='11111111';

+---------------+---------------+----------+---------+


+---------------+---------------+----------+---------+

| 11111111 | J.Brucker | 11111111 | 1000000 |

| 11111112 | Vacation Fund | 11111111 | 1000000 |

| 11111113 | P.Watanapong | 11111120 | 300000 |

| 11111114 | CPE Fund | 11111120 | 1840000 |

+---------------+---------------+----------+---------+

Warning: UPDATE is immediate!

There is no "undo". Changes take effect immediately.

Be Careful! If you forget the WHERE clause it will change all the rows in the table!

sql> UPDATE accounts SET balance=100000 ; /* oops! */

+---------------+---------------+----------+---------+


+---------------+---------------+----------+---------+

| 11111111 | J.Brucker | 11111111 | 1000000 |

| 11111112 | Vacation Fund | 11111111 | 1000000 |

| 11111113 | P.Watanapong | 11111120 | 1000000 |

| 11111114 | CPE Fund | 11111120 | 1000000 |

+---------------+---------------+----------+---------+

Exercise

Get the current population for a city in Thailand.

Search the web or www.ttt.go.th

Update the population in the world database.

Question:

what happens if two people change the same city data (same record) at the same time?

Inserting new records

INSERT adds a new record to a tableINSERT INTO tablename VALUES ( value1, value2, ...);

sql> INSERT INTO Accounts VALUES

('22222222', 'Ample Rich', '00000000' 10000000);

Query OK, 1 row affected.

+---------------+---------------+----------+---------+


+---------------+---------------+----------+---------+

| 22222222 | Ample Rich | 00000000 |10000000 |

+---------------+---------------+----------+---------+

Insert into columns by name

You can specify which columns will receive the values:INSERT INTO tablename (field1, field2, ...)

VALUES ( data1, data2, ...);

sql> INSERT INTO Accounts

(accountNumber, balance, accountName)

VALUES ('22222222', 10000000, 'Ample Rich');


+---------------+---------------+----------+---------+


+---------------+---------------+----------+---------+

| 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', 100000);


The ID field has a qualifier of "AUTO_INCREMENT".

(use "DESCRIBE City")

This means MySQL will assign the ID value itself.

Exercise

View the city data that you just added!

Use UPDATE to change the population of the city you added.

sql> UPDATE City SET population = 95000

WHERE city.name = 'Bangsaen';


sql> SELECT * FROM City WHERE City.name = 'Bangsaen';

How do you get data into a table?

Use INSERT commands (boring).

Put INSERT commands in a Script (text file) and "source" the file (better).

Import command (may depend on DBMS):

LOAD DATA INFILE 'filename' INTO table ...

BCP ("bulk copy" - MS SQL server)

Copying Data Between Tables

Suppose we have another table named NewAccts

NewAccts has accountNumber, accountName, ...

INSERT INTO tablename (field1, field2, ...)

SELECT field1, field2, field3

FROM othertable WHERE condition;

sql> INSERT INTO Accounts

SELECT * FROM NewAccts

WHERE accountNumber NOT NULL;

Relating Tables

The power of a relational database is the ability to selectively combine data from tables. You can use:

select data from multiple tables by matching a field

relations can be 1-to-1 student -> photograph 1-to-many country -> city many-to-1 city -> country many-to-many language -> country

Relational Structure

The Bank.clients table contains bank client information. The primary key is clientID.

sql> DESCRIBE clients;+-----------+-------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+-----------+-------------+------+-----+---------+-------+| clientID | int(11) | | PRI | 0 | || firstName | varchar(40) | | | | || lastName | varchar(40) | | | | || email | varchar(40) | YES | | NULL | |+-----------+-------------+------+-----+---------+-------+

AccountsaccountNumberaccountNameclientIDbalanceavailableBalance

ClientsclientID (KEY)firstNamelastNameemail

clientID

Joining Tables

The power of a database comes from the ability to relate or "join" tables using a condition.

Use "table.field" to qualify a field name:

Accounts.balance, Clients.clientID, ...

The clientID joins the Accounts table and Clients table.

AccountsaccountNumberaccountNameclientIDbalanceavailableBalance

ClientsclientID (KEY)firstNamelastNameemail

Accounts.clientID = Clients.clientID

1*

Joining Tables (2)

Show the balance of all accounts owned by J. Brucker. the account balance is in the Accounts table. the client name is the Clients table. relate the tables using clientID field.

SELECT accountNumber, firstName, balance

FROM Accounts, Clients

WHERE Accounts.clientID = Clients.clientID

AND clients.firstName = 'James';

+---------------+---------------+---------+| accountNumber | firstName | balance |+---------------+---------------+---------+| 11111111 | James | 100000 || 11111112 | James | 22500 |

Exercise

What fields can we use to relate tables in the world database?

CountryCodeNameContinentRegionSurfaceAreaPopulationGNPLocalNameCapital

CityIDNameCountryCodeDistrictPopulation

CountryLanguageCountryCodeLanguageisOfficialPercentage

Example: Join Country and City

SELECT Country.Name, City.Name FROM Country, CityWHERE Country.Code = City.CountryCodeAND Continent = 'South America';

CountryCodeNameContinentRegionSurfaceAreaPopulationGNPLocalNameCapital

CityIDNameCountryCodeDistrictPopulation

Country.Code = City.CountryCode

Exercise

In what countries is the Thai language used?

By what percentage of the people?

Example:

SELECT ...

FROM Country, CountryLanguage

WHERE Country.Code = CountryLanguage.CountryCode

AND ... ;

Use Aliases to Reduce Typing

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 language = 'Chinese'

AND isOfficial = 'T';

L is an alias for

CountryLanguage

you can omit table name when there is no ambiguity

Exercise

What countries use English?

ORDER the results by percentage spoken, from largest to smallest %.

In how many countries is English the official language?

Harder

In the world, approximately how many people speak English?

sum( population * Language.percentage / 100 )

"JOIN"

JOIN joins tables

Many forms:

INNER JOIN (include only matching columns)

OUTER JOIN (include all columns)

LEFT OUTER JOIN

NATURAL JOIN

CONDITION JOIN

Learn them all in a course on database...

Example of a Condition Join

JOIN the CountryLanguage and Language tables using the country code:

SELECT * FROM Country C

JOIN CountryLanguage L

ON C.code = L.countrycode

;

Exercise

JOIN the Country and Language tables.

View Country name and language with "SELECT ..."

How many times is Thailand listed in the results?

How many times is China listed in the results?

How can you order the results by language ?

Multiple Condition Join

You can join many tables at one time:

SELECT CO.name, CI.*, L.language

FROM Country CO

JOIN CountryLanguage L

ON CO.code = L.countrycode

JOIN City CI

ON CO.code = CI.countrycode

WHERE ...; /* more conditions */

Data Definition Commands

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 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. Read the file into mysql: source filename;

CREATE TABLE CUSTOMER (accountNumber VARCHAR(8) NOT NULL,clientID VARCHAR(40) NOT NULL,balance DOUBLE DEFAULT '0',availableBalance DOUBLE DEFAULT '0',PRIMARY KEY( clientID )

) ;

File: /temp/create-table.sql

sql> SOURCE /temp/create-table.sql;


Deleting Records

Use DELETE to delete one or more records

DELETE FROM tablename WHERE condition;

Delete all bank accounts with zero balance

sql> DELETE FROM Accounts WHERE balance <= 0;


Deleting a Table

To delete a table to a database:

DROP TABLE tablename ;

sql> DROP TABLE CUSTOMER ;

Exercise

Delete the city you added to the City table.

On your friend's machine, is it deleted immediately?

Views

A View acts like a "virtual table" containing selected data from one or more real tables.

CountryNameContinentCode...

CountryLanguage

LanguagePercentageisOfficial...

MyViewNameLanguagePercentage

CREATE VIEW MyView AS ...

View Example

Create a view that shows country names, languages, and percentages.

sql> CREATE VIEW lang

AS

SELECT name, language, percentage


WHERE C.code = L.countrycode

ORDER BY language ASC;


sql> SELECT * FROM lang WHERE language='Thai';

Use a view similar to using a table:

Productivity Hint

Type the "CREATE VIEW" statement into a file. Read the file into mysql: source filename;

CREATE VIEW lang AS

SELECT name, language, percentage


WHERE C.code = L.countrycode;

File: /temp/makeview.sql

sql> SOURCE /temp/makeview.sql;


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 ...

list all the databases that you have access to?

use a database?

get information about the structure of a table?

query data in one or more tables?

add new row(s) of data to a table?

change some existing data in rows?

delete some rows of data?

delete an entire table?

SQL Quiz

Database Game

Rules

"largest" and "smallest" refer to size (surfaceArea).

"most populous", "least populous" refer to population

"richest", "poorest" means GNP per capita (population), not total GNP, but the GNP must not be zero (GNP = 0 means no data).

What is the World's Smallest Nation?

How big is it? How many people live there?

What is the Largest Country in Africa?

Show the SQL How big is it?

In what countries is Thai spoken?

SELECT c.name, l.language

FROM Country c

JOIN CountryLanguage l

ON c.code = l.countrycode

WHERE ...

How many nations speak English?

Is English spoken in Thailand? Fix the database.

SELECT COUNT(*)

FROM Country c

JOIN CountryLanguage l

ON c.code = l.countrycode

WHERE ...

What cities are in Thailand ?

Sort them by District

+------+-------------------+-------------------+------------+

| ID | Name | District | Population |

+------+-------------------+-------------------+------------+

| 3320 | Bangkok | Bangkok | 6320174 |

...

Resources

MySQL

http://dev.mysql.com/tech-resources/articles/

Learning SQL

http://www.w3schools.com/sql/ nice tutorial and command reference

Database Access using SQL Very basic introduction James Brucker.

Documents

Transcript of Database Access using SQL Very basic introduction James Brucker.