Databases: basic concepts

Before starting programming in SQL, seek first to understand the world around it. A world composed of databases, data, hard drives, queries.

What is a database?

A database is like a big box containing information.

Once you insert information in a database, you can easily and quickly retrieve, update or delete this information. Even if you have millions and millions of things kept inside.

Example: a database can contain information about a company. Such a database would contain information about the company’s customers, payments, employees…

In this database, you can:

  • insert information when you gain a new customer, a when a new employee joins the company.
  • update information when the customer changes phone number or an employee has a higher salary.
  • retrieve the information when you want to call or mail an existing customer, or get information about a payment.

What is data ?

The information contained in a database is also called data.

How does a database look like ?

A database is invisible for the human eye. It is information recorded on a hard drive. Like a film or music recorded on a DVD.

A hard what?

A hard drive. A hard drive looks like a thin box made of plastic and metal. It is sitting inside a computer. Hard drives store information, like DVD or CD do.

If you look inside this box, you will see something looking like a thick CD turned upside down (you can see one on the left hand side on the picture). In case of more modern hard drives (Solid State Drives: you can see one on the right hand side of the picture), you will see a few microchips glued on a green or blue board.

Why not just keep the information in a text file?

It is more convenient and faster to search and manipulate information with a database, especially if you have a lot of data.

What is an SQL query?

A query is an order given to the database to execute an action, such as:

  • retrieving data.
  • inserting or updating data.
  • deleting data.

You should write this order in a language that the database can understand. One of these languages is SQL. SQL stands for Structured Query Language.
 

To test your understanding of this lesson, take the Database Basic Concepts Quiz. You can also go to the next lesson about Database Tables, Columns and Rows.
 
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Last udpated: September 10, 2017
Created: April 10, 2014