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Databases

MIS105

Irfan Ahmed Ilyas

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More topics on Databases

• Databases Advantages

• Types of Databases

• Databases Uses and Issues

• Writing Queries in DBMS

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Databases Advantages

– Sharing information• One department to another

– Security• Password to access

– Less data redundancy• Excess storage reduced

– Data integrity• Consistent data

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Types of Databases

• Individual database– Integrated files used by one person

• Shared database– Common operational– Common user

• Distributed database• Proprietary database• Web database

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Database Uses and Issues

• Strategic uses

– Data warehouse

– Data mining

• Many databases used everyday

– Business directories

– Business statistical information

– Web search databases

• Security issues

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Writing Queries in DBMS

1. What are Queries?

2. Available Query Types• Data Manipulation Queries• Data Definition Queries

3. Creating Queries in Access1. QBE (Query By Example)2. SQL (Structured Query Language)

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… Competencies

4. Working with SELECT Queries1. Using Single Table

2. Multiple table

3. Parametric (Runtime Criteria) Query

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What Are Queries?

• Queries help the user to select information from tables for a specific purpose

• Queries can– Show the selected fields– Show selected records from one or multiple table– Update selected records– Delete selected records– Make new tables– Append records in an existing table

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Available Query Types

• Data Manipulation Queries• SELECT Queries

– Show database records fulfilling some criteria

• UPDATE Queries– Modify database records (fulfilling some criteria)

• APPEND Queries– Add more database records to some table

• DELETE Queries– Delete some database records fulfilling some criteria

• Data Definition Queries• CREATE TABLE Queries

– Create new table\field types inside the database

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Creating Queries in Access

• QBE (Query By Example) Approach– Allows a visual Query creation

– Query Grid allows to• select records from the required tables\

other queries• select only the desired field of the

records• sort the result on the basis of some field

values• specify record selection criteria

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An Example Query in a QBE Grid

Query showing Saudi Faculty Members

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…Creating Queries in Access

• Using SQL (Structured Query Language) Statements– A standard way of creating Queries – Applicable to all existing DBMS (relational)– A set of statements is used to create

Queries

In Access: View\ SQL View is used to write Queries directly in SQL

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…Creating Queries in Access

• Example SQL StatementsSELECT Queries

– UPDATE Queries

SELECT <field name(s)>

FROM <table name(s)>

WHERE <condition(s)>;

UPDATE <table name(s)> SET <field name= value>

WHERE <condition(s)>;

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An Example Query in SQL View

Query showing Saudi Faculty Members in SQL View

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Working with SELECT Queries• SELECT Queries show

database records fulfilling some criteria

• Query Criteria are defined on one or more field values

• Compound criteria expressions can be made (by using AND/ OR)

Logical Operators for building Query Criteria

Example Criteria Expressions

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Working with SELECT Queries

Compound Criteria Queries (AND \ OR)

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1. SELECT Queries: Single Table

• Query only needs information from a single table

• Example– Faculty information is needed for Saudi Faculty

Query Result

A SELECT Query with single table

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2. SELECT Queries: Multiple Table• Query needs information from more than one tables• All tables used must be properly related to each other

(using PK\ FK links)• Example

– Faculty information including their department name is needed

Query Result

SELECT Query with multiple tables

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….SELECT Queries: Multiple Table• Effect of using tables without any relationships

Employee TableJobs Table

Query Result: Cross Product of Records

Multiple Table Query having no relationship

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3. SELECT Queries: Parametric

• When?– Criteria value is flexible to change during Query runtime

• Example– Faculty information who join the university in a given value

of Year (given during runtime)

Query ResultVariable Value

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