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Databases
MIS105
Irfan Ahmed Ilyas
More topics on Databases
• Databases Advantages
• Types of Databases
• Databases Uses and Issues
• Writing Queries in DBMS
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CE 2
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
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• 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
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• 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
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Data Manipulation Queries
Data Definition Queries
3. Creating Queries in Access
1. QBE (Query By Example)
2. SQL (Structured Query Language)
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… Competencies
4. Working with SELECT Queries
1. 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
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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
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UPDATE Queries
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CREATE TABLE Queries
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Delete some database records fulfilling some criteria
Data Definition Queries
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Add more database records to some table
DELETE Queries
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Modify database records (fulfilling some criteria)
APPEND Queries
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Show database records fulfilling some criteria
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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CE 11
…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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CE 12
…Creating Queries in Access
• Example SQL Statements
SELECT Queries
SELECT <field name(s)>
FROM <table name(s)>
WHERE <condition(s)>;
– UPDATE Queries
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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CE 14
Working with SELECT Queries
• SELECT Queries show
database records
fulfilling some criteria
• Query Criteria are
defined on one or more
field values
Logical Operators for building
Query Criteria
• Compound criteria
expressions can be
made (by using AND/
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Example Criteria
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Expressions CE 15
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
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A SELECT Query with single table
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Query Result
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
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Query Result
SELECT
Query with multiple
tables Companies, Inc.
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….SELECT Queries: Multiple Table
• Effect of using tables without any relationships
Jobs Table
Employee Table
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Query Result: Cross
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Ch 11 Table Query having no relationship
Multiple
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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)
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Query Result
Variable Value
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