Database Management systems and Standardized Query LanguageThe easy way to handle data

Before the Database Management Systems The programmer had to handle all details of

data storage and retrieval Low level programming A new wheel invented all the time All data in flat files with different format Hard to maintain data integrity Hard to handle simultaneous data access

What is a Database Management System (DBMS)? A system for storing data in a standardized

manner A system for retrieving data easily A system for protecting data against failure

and unauthorized access A tool for simplifying system development Relieves the programmer of physical data

storage

Different kind of DBMS

Hierarchical DBMS, 60s Relation DBMS, RDBMS, 70s Object DBMS, 80s Object-relational DBMS, 90s Most databases today are RDBMS or Object-

relational DBMS

Relational Database Systems

Started in the 70s at IBM by Cod Several implementations by companies like

Oracle, Sybase, Upright and Microsoft Highly optimized systems Proven and mature technology Several international standards Most systems today uses a RDBMS

The Relational Model

All data is stored in tables with rows and columns

pnr* name surname sex

1 Fredrik Ålund Male

2 Eva Larsson Female

The Relational Model

Relations between tables and data

pnr* car

1 Volvo

pnr* name

1 Fredrik

2 Eva

The Relational Model

Each column contains atomic data Views is an alternative view of a table Normalization is used to make the data

model as flexible as possible No column should depend on any other column in

the row No redundant data Several levels of normalization and the third

normal form is the most used

Query Languages

No standardized languages in the beginning One query in Oracle would not work in Mimer Hard for the developer to know many

languages No portability Locked into one vendor

Standardized Query Language, SQL SQL is a ISO standard supported by basically

all vendors, more or less SQL 92, SQL 99 and the new SQL 200x SQL is used to create the data model SQL is used to query the database SQL is used to perform updates Powerful language created to manipulate

data

SQL Basics

Tables can be created with the create command C REATE TABLE PERSON(pnr int, namn char(10),

surname char(10), sex char(6)) CREATE TABLE PERSON_CARS(pnr int, car char(7))

Primary keys are defined in the create statement C REATE TABLE PERSON(pnr int, namn char(10),

surname char(10), sex char(6), primary key(pnr))

SQL Basics

Foreign keys can also be defined in the create statement CREATE TABLE PERSON_CARS(pnr int, car

char(7), foreign key(pnr) references PERSON(pnr) on delete cascade)

SQL Basics

A column can have restrictions and default values C REATE TABLE PERSON(pnr int, name

char(10) default ‘Unknown’, surname char(10), sex char(6) not null, primary key(pnr))

SQL Basics

A table can be altered after has been created ALTER TABLE PERSON_CARS ADD

CONSTRAINT person_car_pk PRIMARY KEY(pnr, car)

ALTER TABLE PERSON ADD COLUMN AGE INT

SQL Basics

Data is retrieved with the SELECT statement SELECT * FROM PERSON SELECT PNR, NAME FROM PERSON SELECT * FROM PERSON WHERE AGE > 25

AND SEX=‘Male’ Tables are joined in the SELECT statement

SELECT PERSON.NAME, PERSON_CARS.CAR FROM PERSON, PERSON_CARS WHERE PERSON.PNR = PERSON_CARS.PNR

SQL Basics

Joins can also be performed with the JOIN condition SELECT PERSON.NAME, PERSON_CARS.CAR

FROM PERSON LEFT OUTER JOIN PERSON_CARS ON PERSON.PNR=PERSON_CARS.PNR

Gives all person and their car. If they don’t have a car, null is returned in that columns instead. In our case, Fredrik, Volvo and Eva, null

SQL Basics

SELECT PERSON.NAME, PERSON_CARS.CAR FROM PERSON RIGHT OUTER JOIN PERSON_CARS ON PERSON.PNR=PERSON_CARS.PNR Gives all person and their car only if they have a

car In our case, Fredrik, Volvo SELECT PERSON.NAME,

PERSON_CARS.CAR FROM PERSON NATURAL JOIN PERSON_CARS The same result as above

SQL Basics

Data is inserted with the INSERT statement INSERT INTO PERSON(pnr, name, surname,sex,

age) VALUES(3, ‘Eva’, ‘Larsson’, ‘Female’, ’27’) INSERT INTO PERSON_CARS(pnr, car)

VALUES(3,’Toyota’)

SQL Basics

Data can be update with the UPDATE statements UPDATE PERSON SET AGE=22 WHERE

PNR=1 Update Fredriks age to 22

UPDATE PERSON_CAR SET CAR=‘Volvo’ Updates all cars to Volvo

SQL Basics

Data is deleted with the DELETE statement DELETE FROM PERSON WHERE ID=3

Deletes the row with Eva Larsson

SQL Basics

Views are created with a combination of a CREATE and a SELECT CREATE VIEW VOLVO_OWNERS(pnr, name,

surname, sex, age) as SELECT p.pnr, name, surname, sex, age FROM PERSON p, PERSON_CARS pc WHERE pc.pnr=p.pnr AND pc.cars=‘Volvo’ Only show Volvo users SELECT * FROM VOLVO_OWNERS

Advanced SQL

Stored Procedures A precompiled query in the database. Entire

systems can be built with Stored Procedures. Triggers

Certain events can trigger actions, for example a stored procedure might be started when a row is deleted

Both Stored Procedures and Triggers are part of SQL 99

Transactions

Transactions is the way that the RDBMS keeps the data consistent A transaction is supposed to have the ACID

property Atomic Consistent Isolated Durable

Transactions

The classic example is the cash machine If the cash machine gives out the money, but the

reduce balance doesn’t finnish, we have too much mony

If the balance is reduced but we don’t get any money we have too little

Check balance

Okej, give the money

Reduce balance

Cash machine

Bank

Transactions in SQL

A transaction is started with START A transaction is commited with COMMIT

If ok, everything is secured and well A transaction is rolled back (undone) with

ROLLBACK All operations are undone