dbms fundamental concepts telerik software academy databases
TRANSCRIPT
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Database Systems
DBMS Fundamental Concepts
Telerik Software Academyhttp://academy.telerik.com
Databases
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Table of Contents1. Database Models
2. Relational Database Model
3. DBMS & RDBMS Systems
4. Tables, Relationships, Multiplicity, E/R Diagrams
5. Normalization
6. Constraints
7. Indices
8. The SQL language2
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Table of Contents (2)9. Stored Procedures
10.Views
11.Triggers
12.Transactions and Isolation Levels
13.NoSQL Databases
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RDBMS SystemsRelational Databases, Database Servers
and RDBMS
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Relational Databases Database models
Hierarchical (tree) Network / graph Relational (table) Object-oriented
Relational databases Represent a bunch of tables
together with the relationships between them
Rely on a strong mathematical foundation: the relational algebra
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Relational Database Management System
(RDBMS) Relational Database Management Systems (RDBMS) manage data stored in tables
RDBMS systems typically implement Creating / altering / deleting tables
and relationships between them (database schema)
Adding, changing, deleting, searching and retrieving of data stored in the tables
Support for the SQL language Transaction management (optional)
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RDBMS Systems RDBMS systems are also known as:
Database management servers Or just database servers
Popular RDBMS servers: Microsoft SQL Server Oracle Database MySQL IBM DB2 PostgreSQL SQLite
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Tables and RelationshipsDatabase Tables, Relationships,
Multiplicity
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Database tables consist of data, arranged in rows and columns For example (table Persons):
All rows have the same structure Columns have name and type
(number, string, date, image, or other)
Id First Name
Last Name
Employer
1 Svetlin Nakov Telerik
2 Stephen Forte Telerik
3 Steve Jobs Apple
Tables
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Table Schema The schema of a table is an ordered sequence of column specifications (name and type)
For example the Persons table has the following schema:
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Persons ( Id: number, FirstName: string, LastName: string, Employer: string)
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Primary Key Primary key is a column of the table
that uniquely identifies its rows (usually its is a number)
Two records (rows) are different if and only if their primary keys are different
The primary key can be composed by several columns (composite primary key)
Id First Name
Last Name
Employer
1 Svetlin Nakov Telerik
2 Stephen Forte Telerik
3 Steve Jobs Apple
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Primary key
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Relationships Relationships between tables are based on interconnections: primary key / foreign key
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Id Name CountryId1 Sofia 12 Plovdiv 13 Munich 24 Berlin 25 Moscow 3
Id Name1 Bulgari
a2 German
y3 Russia
Towns
Countries
Primary key Prima
ry key
Foreign key
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Relationships (2) The foreign key is an identifier of a
record located in another table (usually its primary key)
By using relationships we avoid repeating data in the database In the last example the name of the
country is not repeated for each town (its number is used instead)
Relationships have multiplicity: One-to-many – e.g. country / towns
Many-to-many – e.g. student / course
One-to-one – e.g. example human / student
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Relationships' Multiplicity
Relationship one-to-many (or many-to-one) A single record in the first table has
many corresponding records in the second table
Used very often
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Id Name CountryId
1 Sofia 12 Plovdiv 13 Munich 24 Berlin 25 Moscow 3
Id Name1 Bulgaria2 German
y3 Russia
Towns
Countries
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Relationships' Multiplicity (2)
Relationship many-to-many Records in the first table have many
correspon-ding records in the second one and vice versa
Implemented through additional table
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Id Name
1 Pesho2 Minka3 Gosho4 Penka
Id Name
1 .NET2 Java3 PHP
StudentsCourses
StudentId
CourseId
1 1
1 2
3 2
3 3
4 2
StudentsCourses
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Id Title1 Ph.D.
Relationships' Multiplicity (3)
Relationship one-to-one A single record in a table corresponds
to a single record in the other table
Used to model inheritance between tables
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Id Name Age1 Ivan
Daddy72
2 Goiko Dude
26
3 Grand Mara
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Persons
Id Specialty2 Computer
Science
3 Chemistry
Students
Primary & Foreign key in the same time
Primary key
Primary & foreign key in the same time
Professors
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Representing Hierarchical Data
How do we represent trees and graphs?
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Root
Documents
Pictures
Birthday Party
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Self-Relationships The primary / foreign key relationships can point to one and the same table Example: employees in a company
have a manager, who is also an employee
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Id Folder ParentId1 Root (null)2 Documents 13 Pictures 14 Birthday Party 3
EmployeesPrimary key
Foreign key
Self-relations
hip
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E/R DiagramsEntity / Relationship
Diagrams and DB Modeling Tools
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Relational Schema Relational schema of a DB is the collection of: The schemas of all tables
Relationships between the tables
Any other database objects (e.g. constraints)
The relational schema describes the structure of the database Doesn't contain data, but metadata
Relational schemas are graphically displayed in Entity / Relationship diagrams (E/R Diagrams)
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E/R Diagrams – Examples
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The diagram is created with
Microsoft SQL Server
Management Studio
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E/R Diagrams – Examples (2)
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The diagram
is created
with ERwin
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E/R Diagrams – Examples (3)
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The diagram is created with fabFORCE DB Designer for
MySQL
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E/R Diagrams – Examples (4)
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Department
PK DeptId
DeptName
Professor
PK,FK1 ProfessorId
Title
DepartmentProfessor
PK,FK1 DeptIdPK,FK2 ProfessorId
Student
PK,FK1 StudentId
FacultyNumber
Course
PK CourseId
CourseNameFK1 DeptIdFK2 ProfessorId
CourseStudent
PK,FK1 StudentIdPK,FK2 CourseId
Person
PK PersonId
FirstNameLastName
The diagram is created with MS
Visio
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Tools for E/R Design Data modeling tools allow building E/R diagrams, generate / import DB schemas: SQL Server Management Studio
MySQL Workbench
Oracle JDeveloper
Microsoft Visio
CASE Studio
Computer Associates ERwin
IBM Rational Rose 25
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DB NormalizationAvoiding Duplicated Data
through Database Schema Normalization
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Normalization Normalization of the relational schema removes repeating data
Non-normalized schemas can contain many data repetitions, e.g.
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Product Producer
Price
Category Shop Town
yoghurt Mlexis Ltd. 0.67 food
store "Mente
"Sofia
bread "Dobrudja"
Bakery "Smoky" 0.85 food
store "Mente
"Sofia
beer "Zagorka"
Zagorka Corp. 0.68 soft
drinks
stall "non-stop"
Varna
beer "Tuborg"
Shoumen Drinks Corp.
0.87 soft drinks
stall "non-stop"
Varna
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Normalization (6) Example of fully normalized schema (in 4th Normal Form):
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Id
Name
2 "Milk" Ltd.
4 "Zagorka" AD
Id
Name
4 beer
2 food
Id Product ProducerId Price
CategoryI
d
ShopId
TownId
1 Youghurt 2 0.67 2 4 1
2 bread "Dobrudja" 3 0.55 2 4 1
3 rakia "Peshtera" 6 4.38 5 2 1
4 beer "Tuborg" 4 0.67 4 1 3I
dName
1 Billa
4 METRO
Id
Name
1 Sofia
3 Varna
Products
Producers Categories Shops Towns
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Other Database ObjectsConstraints, Indices, SQL,
Stored Procedures, Views, Triggers
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Integrity Constraints Integrity constraints ensure data integrity in the database tables Enforce data rules which cannot be
violated Primary key constraint
Ensures that the primary key of a table has unique value for each table row
Unique key constraint Ensures that all values in a certain
column (or a group of columns) are unique
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Integrity Constraints (2)
Foreign key constraint Ensures that the value in given
column is a key from another table Check constraint
Ensures that values in a certain column meet some predefined condition
Examples:
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(hour >= 0) AND (hour < 24)
name = UPPER(name)
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Indices Indices speed up searching of values in a certain column or group of columns
Usually implemented as B-trees
Indices can be built-in the table (clustered) or stored externally (non-clustered)
Adding and deleting records in indexed tables is slower!
Indices should be used for big tables only (e.g. 50 000 rows)
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The SQL Language SQL (Structured Query Language)
Standardized declarative language for manipulation of relational databases
SQL-99 is currently in use in most databases
http://en.wikipedia.org/wiki/SQL#Standardization
SQL language supports: Creating, altering, deleting tables
and other objects in the database Searching, retrieving, inserting,
modifying and deleting table data (rows)
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The SQL Language (2) SQL consists of:
DDL – Data Definition Language CREATE, ALTER, DROP commands
DML – Data Manipulation Language SELECT, INSERT, UPDATE, DELETE
commands
Example of SQL SELECT query:
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SELECT Towns.Name, Countries.NameFROM Towns, CountriesWHERE Towns.CountryId = Countries.Id
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Stored Procedures
Stored procedures (database-level procedures) Consist of SQL-like code stored in
the database Code executed inside the database
server Much faster than an external code Data is locally accessible Can accept parameters Can return results
Single value
Record sets
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Stored Procedures (2) Stored procedures are written in a
language extension of SQL T-SQL – in Microsoft SQL Server PL/SQL – in Oracle
Example of stored procedure in Oracle PL/SQL:
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CREATE OR REPLACE PROCEDURE spInsertCountry(countryName varchar2) ISBEGIN INSERT INTO Countries(Name) VALUES(countryName);END;
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Views
Views are named SQL SELECT queries which are used as tables Simplify data access Facilitate writing of complex SQL
queries
Used also to apply security restrictions: E.g. a certain user isn't given
permissions on any of the tables in the database
The user is given permissions on few views (subset of DB) and few stored procedures only
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Views – Example
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Id Company TownId
1 Mente LTD 1
2 BulkSoft Inc.
2
3 HardSoft Corp.
4
4 Sputnik Corp.
3
Id Town CountryId
1 Sofia 1
2 New York
3
3 Moscow
2
4 Plovdiv 1
Companies Towns
Id Country
1 Bulgaria
2 Russia
3 USA
Countries
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Views – Example (2)
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CREATE VIEW V_BGCompanies AS SELECT Companies.Id AS Id, Companies.Company AS Company FROM Companies INNER JOIN (Towns INNER JOIN Countries ON Towns.CountryId = Countries.Id) ON Companies.TownId = Towns.Id WHERE Countries.Country = "Bulgaria";
Id Company1 Mente Ltd.
3 HardSoft Corp.V_BGCompanies
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Triggers Triggers are special stored procedures that are activate when some event occurs, for instance: When inserting a record When changing a record When deleting a record
Triggers can perform additional data processing of the affected rows, e.g. To change the newly added data To maintain logs and history
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Triggers – Example
We have a table holding company names:
A trigger that appends "Ltd." at the end of the name of a new company:
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CREATE TABLE Companies( Id number NOT NULL, Name varchar(50) NOT NULL)
CREATE OR REPLACE TRIGGER trg_Companies_INSERT BEFORE INSERT ON Company FOR EACH ROWBEGIN :NEW.Name := :NEW.Name || ' Ltd.';END;
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TransactionsACID Transactions and Isolation
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Transactions
Transactions are a sequence of database operations which are executed as a single unit: Either all of them execute
successfully Or none of them is executed at all
Example: A bank transfer from one account
into another (withdrawal + deposit) If either the withdrawal or the
deposit fails the entire operation should be cancelled
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Rollback
Commit
DB Transactions Lifecycle
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Read Write
Write
Durable
starting state
Durable,consisten
t,ending state
Sequence of reads
and writes
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Transactions Behavior Transactions guarantee the consistency and the integrity of the database All changes in a transaction are
temporary Changes become final when
COMMIT is successfully executed At any time all changes done in the
transaction can be canceled by executing ROLLBACK
All operations are executed as a single unit Either all of them pass or none of
them
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NoSQL DatabasesNon-Relational Database Systems
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Non-Relational Data Models
Document model Set of documents, e.g. JSON strings
Key-value model Set of key-value pairs
Hierarchical key-value Hierarchy of key-value pairs
Wide-column model Key-value model with schema
Object model Set of OOP-style objects
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What is NoSQL Database?
NoSQL (non-relational) databases Use document-based model (non-
relational) Schema-free document storage
Still support CRUD operations(create, read, update, delete)
Still support indexing and querying
Still supports concurrency and transactions
Highly optimized for append / retrieve
Great performance and scalability NoSQL == “No SQL” or “Not Only
SQL”?
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Relational vs. NoSQL Databases
Relational databases Data stored as table rows
Relationships between related rows
Single entity spans multiple tables
RDBMS systems are very mature, rock solid
NoSQL databases Data stored as documents
Single entity (document) is a single record
Documents do not have a fixed structure
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Relational vs. NoSQL Models
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Name: Svetlin Nakov
Gender: male
Phone: +359333777555
Address:
- Street: Al. Malinov 31
- Post Code: 1729
- Town: Sofia
- Country: Bulgaria
Email: [email protected]
Site: www.nakov.com
Document ModelRelational Model
Name Svetlin Nakov
Gender male
Phone +359333777555
Email [email protected]
Site www.nakov.com
Country Bulgaria
Street Al. Malinov 31
Post Code
1729
Town Sofia
*1
*1
*1
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NoSQL Database Systems
Redis Ultra-fast in-memory data
structures server
MongoDB Mature and powerful JSON-
document database
CouchDB JSON-based document database
with REST API
Cassandra Distributed wide-column database
DB Ranking: http://db-engines.com/en/ranking
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Questions?
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Database Systems
http://academy.telerik.com
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Exercises1. What database models do you know?
2. Which are the main functions performed by a Relational Database Management System (RDBMS)?
3. Define what is "table" in database terms.
4. Explain the difference between a primary and a foreign key.
5. Explain the different kinds of relationships between tables in relational databases.
6. When is a certain database schema normalized? What are the advantages of normalized databases?
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Exercises (2)7. What are database integrity constraints
and when are they used?
8. Point out the pros and cons of using indexes in a database.
9. What's the main purpose of the SQL language?
10.What are transactions used for? Give an example.
11.What is a NoSQL database?
12.Explain the classical non-relational data models.
13.Give few examples of NoSQL databases and their pros and cons.
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