Normalization

What's Database Normalization ?
Normalization is the process where a database is designed in a way that removes redundancies, and increases the clarity in organizing data in a database.
In easy English, it means take similar stuff out of a collection of data and place them into tables. Keep doing this for each new table recursively and you'll have a Normalized database. From this resultant database you should be able to recreate the data into it's original state if there is a need to do so.
The important thing here is to know when to Normalize and when to be practical. That will come with experience. For now, read on...
Normalization of a database helps in modifying the design at later times and helps in being prepared if a change is required in the database design. Normalization raises the efficiency of the database in terms of management, data storage and scalability.
Now Normalization of a Database is achieved by following a set of rules called 'forms' in creating the database.
These rules are 5 in number (with one extra one stuck in-between 3&4) and they are:
1st Normal Form or 1NF:
Each Column Type is Unique.
2nd Normal Form or 2NF:
The entity under consideration should already be in the 1NF and all attributes within the entity should depend solely on the entity's unique identifier.
3rd Normal Form or 3NF:
The entity should already be in the 2NF and no column entry should be dependent on any other entry (value) other than the key for the table.
If such an entity exists, move it outside into a new table.
Now if these 3NF are achieved, the database is considered normalized. But there are three more 'extended' NF for the elitist.
These are:
BCNF (Boyce & Codd):
The database should be in 3NF and all tables can have only one primary key.
4NF:
Tables cannot have multi-valued dependencies on a Primary Key.
5NF:
There should be no cyclic dependencies in a composite key.
Well this is a highly simplified explanation for Database Normalization. One can study this process extensively though. After working with databases for some time you'll automatically create Normalized databases. As, it's logical and practical.
For now, don't worry too much about Normalization. The quickest way to grasp SQL and Databases is to plunge headlong into creating tables and start messing around with SQL statements. After you go through the tutorial examples and also the example contacts database, look at the example provided in creating a normalized database near the very end of this tutorial. And then try to think how you would like to create your own database.
Much of database design depends on how YOU want to keep the data. In real life situations often you may find it more convenient to store data in tables designed in a way that does fall a bit short of keeping all the NFs happy. But that's what databases are all about. Making your life simpler.



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SQL Basics

What's SQL ?
In 1971, IBM researchers created a simple non-procedural language called Structured English Query Language. or SEQUEL. This was based on Dr. Edgar F. (Ted) Codd's design of a relational model for data storage where he described a universal programming language for accessing databases.
In the late 80's ANSI and ISO (these are two organizations dealing with standards for a wide variety of things) came out with a standardized version called Structured Query Language or SQL. SQL is pronounced as 'Sequel'. There have been several versions of SQL and the latest one is SQL-99. Though SQL-92 is the current universally adopted standard.
SQL is the language used to query all databases. It's simple to learn and appears to do very little but is the heart of a successful database application. Understanding SQL and using it efficiently is highly imperative in designing an efficient database application. The better your understanding of SQL the more versatile you'll be in getting information out of databases.

There are four basic commands which are the workhorses for SQL and figure in almost all queries to a database.
INSERT - Insert Data
DELETE - Delete Data
SELECT - Pull Data
UPDATE - Change existing Data
As you can see SQL is like English.
Let's build a real world example database using MySQL and perform some SQL operations on it.
A database that practically anyone could use would be a Contacts database.
In our example we are going to create create a database with the following fields:
• FirstName
• LastName
• BirthDate
• StreetAddress
• City
• State
• Zip
• Country
• TelephoneHome
• TelephoneWork
• Email
• CompanyName
• Designation
First, lets decide how we are going to store this data in the database. For illustration purposes, we are going to keep this data in multiple tables.

This will let us exercise all of the SQL commands pertaining to retrieving data from multiple tables. Also we can separate different kinds of entities into different tables. So let's say you have thousands of friends and need to send a mass email to all of them, a SELECT statement (covered later) will look at only one table.
Well, we can keep the FirstName, LastName and BirthDate in one table.
Address related data in another.
Company Details in another.
Emails can be separated into another.
Telephones can be separated into another.



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Database

What's a database ?
A database is a collection of data organized in a particular way.
Databases can be of many types such as Flat File Databases, Relational Databases, Distributed Databases etc.

What a DBMS ?
MySQL and mSQL are database management systems or DBMS. These software packages are used to manipulate a database. All DBMSs use their own implementation of SQL. It may be a subset or a superset of the instructions provided by SQL 92.
MySQL, due to it's simplicity uses a subset of SQL 92 (also known as SQL2).

What's an RDBMS ?
This concept was first described around 1970 by Dr. Edgar F. Codd in an IBM research publication called "System R4 Relational".
A relational database uses the concept of linked two-dimensional tables which comprise of rows and columns. A user can draw relationships between multiple tables and present the output as a table again. A user of a relational database need not understand the representation of data in order to retrieve it. Relational programming is non-procedural.

What's procedural and non-procedural ?
Programming languages are procedural if they use programming elements such as conditional statements (if-then-else, do-while etc.). SQL has none of these types of statements.
In 1979, Relational Software released the world's first relational database called Oracle V.2




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