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Overview of Databases

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Content

Databases Example: Access Structure Query language (SQL)

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What is a Database?

Database is an organized collection of related data, typically stored on disk, and accessible by possibly many concurrent users.

Have programming capability to access and manipulate data

Three traditional types of database: hierarchical relational (most prevalent type) network New: object-oriented

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Database

Example databases: Oracle Sybase/Microsoft SQL IBM’s DB2, IMS and SQL/DS dBase Access

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Database

Relational database: It is a tabular database in which the data is

defined so that it can reorganized and accessed in a number of different ways.

Tables are used to make it easy to maintain and data

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Database

Advantage of relational databases: easy to create easy to access easy to extend

Possible disadvantage Limited set of content (compared to object

oriented databases).

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Database

Relational database structure: set of tables containing data fitted into predefined

categories; each table (relation) contains one or more data

categories in columns. each row contains a unique instance of data for

the categories defined by column.

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Programming

Database systems also have some programming capability

Often using SQL (see later) Allows for accessing and manipulating data

to form a report or to answer a query.

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Access

Relational database Integrates data from spreadsheet and other

database User friendly Easy to use (help wizard) Limited in scale of application (small

applications best)

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Features of Access

Database Wizard Simple Query Wizard Filter by selection Integration with Form, filter by form Report output

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Relationships in Access

Multiple tables in one database Matching key fields between table

A key is usually a field with the same name in both tables.

Such key is primary key for one table, foreign key in the other table.

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Access : DatabaseNote: tables, queries, forms and reports.

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Access: Table

Table is where the data is kept

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Access: key

Need to have a key to link data across tables

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Access: Macros and Modules A macro is a set of one or more actions that each perform

a particular operation, such as opening a form or printing a report.

Macros can help to automate common tasks. For example, a macro can run to prints a report when a user clicks a command button.

Module A module is a collection of Visual Basic for Applications

declarations and procedures that are stored together as a unit.

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Access: Report

Predefined report can be generated on demandfrom data.

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Database Programming

Access can use VBA or SQL for programming.

VBA not a standard. SQL (see later) is used by most database

systems.

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SQL

SQL: Structured Query Language It is used to query from and update database. Systems using SQL:

Oracle Sybase Microsoft SQL server Access

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SQL

Standard SQL commands: Select Insert Update Delete Create

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SQL Example

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SQL Example

To find out the ‘Category name’ when ‘Category ID’ equals to 1

SELECT Category name FROM Categories WHERE Category ID=1

Note: ‘Category name’ and ‘Category ID’ are column/field,

‘Categories’ is the table