Sunday, 15 November 2009

Relational Databases

Databases are the most efficient way to store large amounts of information. They emerged in the corporate world when it slowly became obvious that different departments were storing the same information in different places and, perhaps even worse, in different ways.

Databases allowed organisations to store all of that information in one place. Each company created a single central database which was then accessible to different parts of the organisation. Various different people and various different applications were all able to use it. This was far more efficient and opened up lots of new possibilities for businesses.

The data in databases is stored in tables. Most databases consist of a series of linked tables. Each piece of data is placed in relation to the other bits of information in the database, hence the name relational.

When you are creating a database it is important to start of by thinking about the relationships between the different pieces of information that you want to store. This is called the entity relationship model.

Users find information in a database using a software called Database Management Systems (DBMS). Most databases are managed using Structured Query Language (SQL). This is the language that the user has to use to 'ask' the database to find a particular piece of information.

The following is an example of an SQL Query.

select title, year_published, isbn, pubid from titles where year_published >= 1980
order by year_published asc;

This would give you the title, year of publication, ISBN and PubID for any titles in the database which were published after 1980. The list would be in chronological order.

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