DAY 12:DATABASE CONCEPT

Tazin AfrinTazin.Afrin@mail.wvu.edu

September 26, 2013

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DATABASE

• An organized collection of data.• Database supports processes requiring

information about that data.• Example :

– Address book– Record of all employees of CNN international

on their payroll

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DBMS

• Database Management System contains information about a particular enterprise– Collection of interrelated data– Set of programs to access the data – An environment that is both convenient and efficient to

use

• Examples of DBMS :– MySQL– SQLite– Microsoft SQL Server– Microsoft Access

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DBMS

• Database Applications:– Banking: all transactions– Airlines: reservations, schedules– Universities: registration, grades– Sales: customers, products, purchases– Manufacturing: production, inventory, orders,

supply chain– Human resources: employee records,

salaries, tax deductions

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RELATIONAL DATABASE

• A relational database is a collection of data items organized as a set of formally described tables from which data can be accessed easily.

• There are relationships between tables.• Example :

– Microsoft Access

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SAMPLE RELATIONAL DATABASE

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TERMINOLOGY

• Record– In the context of a relational database, a row—also

called a record or tuple—represents a single, implicitly structured data item in a table.

– Each record represents a set of related data– Every record has the same structure.

• Field– Each piece of data in a record is a field– Some fields are required for each record, others are

optional

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RECORDS AND FIELDS

RecordField

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PRIMARY KEY

• A table typically has a column or combination of columns that contain values that uniquely identify each row in the table. This column, or columns, is called the primary key of the table.– A table can contain only one primary key

constraint.

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FOREIGN KEY

• A foreign key is a column or combination of columns that is used to establish and enforce a link between the data in two tables.

• It controls the data that can be stored in the another table.

• A link is created between two tables when the column that hold the primary key value for one table are referenced by the column in another table.

• This column becomes a foreign key in the second table.

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FOREIGN KEY

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FOREIGN KEY

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INDEXES

• Indexes are an ordering of a key or other field that is computed on creation and kept up to date as the database is updated

• By using the index, the database software is able to quickly retrieve the record given the field value

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RELATIONSHIPS

• By including a the key from one table as a field in a different table, we create a relationship between the two tables

• This allows us to link the data between two tables

• Relationships enable you to prevent redundant data.

• 4 kinds of relationships

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RELATIONSHIPS

One to one One to many

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RELATIONSHIPS

Many to one Many to many

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REFERENTIAL INTEGRITY

• Make sure that relationships between records in related tables are valid.

• Ensures that you do not accidentally delete or change related data.

• You cannot enter a value in the foreign key field of the related table that does not exist in the primary key of the primary table.– Cannot enter new account in the account table for a

customer who does not exists.– But can enter new account with NULL value in

customer ID

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CASCADING

• You can specify whether you want to automatically cascade update or cascade delete related records from different tables.– Deletes: If the original record is deleted, the

foreign key record is deleted– Updates: If the key of the original record is

changed, the foreign key is updated to match

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NORMALIZATION

• Normalization is a process of organizing fields and tables to minimize redundancy of data– DRY (don’t repeat yourself)– If you repeat yourself, when you need to

make a change you have to change it everywhere or you will have problems

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SQL

• SQL is structured query language• SQL is how Access interacts with data under

the hood• Queries:

– INSERT INTO ‘table’ VALUES (‘value1’, ‘value2’)– UPDATE ‘table’ SET ‘field1’ = ‘value1’ WHERE

‘field2’ = ‘value2’– DELETE FROM ‘table’ WHERE ‘field’ = ‘value’– SELECT ‘field1’ FROM ‘table’ WHERE ‘field2’ =

‘value’

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EXAM 1

• Student ID is required• If you need accommodations, please make

your request today.• Arrive 15 minutes early• 10 minutes before scheduled class time,

test instructions will be distributed• You may begin at your scheduled class time• You will have 60 minutes

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EXAM 1

• 1st October• Section 58 : at 1:00 pm• Section 60 : at 2:30 pm

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