SQL- Introduction to SQL database

Introduction toIntroduction to
MySQLMySQL

IntroductionIntroduction
• Purpose of Database Systems
• View of Data
• Data Models
• Data Definition Language
• Data Manipulation Language
• Transaction Management
• Storage Management
• Database Administrator
• Database Users
• Overall System Structure

Database ManagementDatabase Management
System (DBMS)System (DBMS)
• Collection of interrelated data
• Set of programs to access the data
• DBMS contains information about a particular enterprise
• DBMS provides an environment that is both convenient and
efficient to use.
• Database Applications:
o Banking: all transactions
o Airlines: reservations, schedules
o Universities: registration, grades
o Sales: customers, products, purchases
o Manufacturing: production, inventory, orders, supply chain
o Human resources: employee records, salaries, tax deductions
• Databases touch all aspects of our lives

Purpose of DatabasePurpose of Database
SystemSystem
• In the early days, database applications were built on top of file
systems
• Drawbacks of using file systems to store data:
o Data redundancy and inconsistency
• Multiple file formats, duplication of information in different files
o Difficulty in accessing data
• Need to write a new program to carry out each new task
o Data isolation — multiple files and formats
o Integrity problems
• Integrity constraints (e.g. account balance > 0) become part
of program code
• Hard to add new constraints or change existing ones

Purpose of DatabasePurpose of Database
Systems (Cont.)Systems (Cont.)
• Drawbacks of using file systems (cont.)
o Atomicity of updates
• Failures may leave database in an inconsistent state with partial
updates carried out
• E.g. transfer of funds from one account to another should either
complete or not happen at all
o Concurrent access by multiple users
• Concurrent accessed needed for performance
• Uncontrolled concurrent accesses can lead to inconsistencies
o E.g. two people reading a balance and updating it at the
same time
o Security problems
• Database systems offer solutions to all the above problems

Levels of AbstractionLevels of Abstraction
• Physical level describes how a record (e.g., customer) is
stored.
• Logical level: describes data stored in database, and
the relationships among the data.
type customer = record
name : string;
street : string;
city : integer;
end;
• View level: application programs hide details of data
types. Views can also hide information (e.g., salary) for
security purposes.

View of DataView of Data
An architecture for a database system

Instances and SchemasInstances and Schemas
• Similar to types and variables in programming languages
• Schema – the logical structure of the database
o e.g., the database consists of information about a set of customers and accounts
and the relationship between them)
o Analogous to type information of a variable in a program
o Physical schema: database design at the physical level
o Logical schema: database design at the logical level
• Instance – the actual content of the database at a particular point in time
o Analogous to the value of a variable
• Physical Data Independence – the ability to modify the physical schema without
changing the logical schema
o Applications depend on the logical schema
o In general, the interfaces between the various levels and components should be
well defined so that changes in some parts do not seriously influence others.

Data ModelsData Models
• A collection of tools for describing
o data
o data relationships
o data semantics
o data constraints
• Entity-Relationship model
• Relational model
• Other models:
o object-oriented model
o semi-structured data models
o Older models: network model and hierarchical model

Entity-RelationshipEntity-Relationship
ModelModel
Example of schema in the entity-relationship model

Entity Relationship ModelEntity Relationship Model
(Cont.)(Cont.)
• E-R model of real world
o Entities (objects)
• E.g. customers, accounts, bank branch
o Relationships between entities
• E.g. Account A-101 is held by customer Johnson
• Relationship set depositor associates customers with accounts
• Widely used for database design
o Database design in E-R model usually converted to design in the
relational model (coming up next) which is used for storage and
processing

Data Definition LanguageData Definition Language
(DDL)(DDL)
• Specification notation for defining the database schema
o E.g.
create table account (
account-number char(10),
balance integer)
• DDL compiler generates a set of tables stored in a data dictionary
• Data dictionary contains metadata (i.e., data about data)
o database schema
o Data storage and definition language
• language in which the storage structure and access methods
used by the database system are specified
• Usually an extension of the data definition language

Data ManipulationData Manipulation
Language (DML)Language (DML)
• Language for accessing and manipulating the data
organized by the appropriate data model
o DML also known as query language
• Two classes of languages
o Procedural – user specifies what data is required and how to get
those data
o Nonprocedural – user specifies what data is required without
specifying how to get those data
• SQL is the most widely used query language

SQLSQL
• SQL: widely used non-procedural language
o E.g. find the name of the customer with customer-id 192-83-7465
select customer.customer-name
from customer
where customer.customer-id = ‘192-83-7465’
o E.g. find the balances of all accounts held by the customer with customer-
id 192-83-7465
select account.balance
from depositor, account
where depositor.customer-id = ‘192-83-7465’ and
depositor.account-number = account.account-number
• Application programs generally access databases through one of
o Language extensions to allow embedded SQL
o Application program interface (e.g. ODBC/JDBC) which allow SQL queries
to be sent to a database

Database UsersDatabase Users
• Users are differentiated by the way they expect to interact with the
system
• Application programmers – interact with system through DML calls
• Sophisticated users – form requests in a database query language
• Specialized users – write specialized database applications that do
not fit into the traditional data processing framework
• Naïve users – invoke one of the permanent application programs
that have been written previously
o E.g. people accessing database over the web, bank tellers,
clerical staff

Database AdministratorDatabase Administrator
• Coordinates all the activities of the database system; the
database administrator has a good understanding of the
enterprise’s information resources and needs.
• Database administrator's duties include:
o Schema definition
o Storage structure and access method definition
o Schema and physical organization modification
o Granting user authority to access the database
o Specifying integrity constraints
o Acting as liaison with users
o Monitoring performance and responding to changes in
requirements

Transaction ManagementTransaction Management
• A transaction is a collection of operations that
performs a single logical function in a database
application
• Transaction-management component ensures that
the database remains in a consistent (correct) state
despite system failures (e.g., power failures and
operating system crashes) and transaction failures.
• Concurrency-control manager controls the
interaction among the concurrent transactions, to
ensure the consistency of the database.

Storage ManagementStorage Management
• Storage manager is a program module that
provides the interface between the low-level data
stored in the database and the application
programs and queries submitted to the system.
• The storage manager is responsible to the following
tasks:
o interaction with the file manager
o efficient storing, retrieving and updating of data

Overall System StructureOverall System Structure

Application ArchitecturesApplication Architectures
Two-tier architecture: E.g. client programs using ODBC/JDBC to
communicate with a database
Three-tier architecture: E.g. web-based applications, and
applications built using “middleware”

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SQL- Introduction to SQL database

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