1 Overview of Databases

2 Content Databases Example: Access Structure Query language (SQL)

3 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

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

5 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

6 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).

7 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.

8 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.

9 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)

10 Features of Access Database Wizard Simple Query Wizard Filter by selection Integration with Form, filter by form Report output

11 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.

12 Access : Database Note: tables, queries, forms and reports.

13 Access: Table Table is where the data is kept

14 Access: key Need to have a key to link data across tables

15 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.

16 Access: Report Predefined report can be generated on demand from data.

17 Database Programming Access can use VBA or SQL for programming. VBA not a standard. SQL (see later) is used by most database systems.

18 SQL SQL: Structured Query Language It is used to query from and update database. Systems using SQL: Oracle Sybase Microsoft SQL server Access

19 SQL Standard SQL commands: Select Insert Update Delete Create

20 SQL Example

21 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