In relational database design, there is a concept of database normalization or simply normalization, which is a process of organizing columns (attributes) and tables (relations) to reduce data redundancy and improve data integrity. (as written on Wikipedia).
As most articles are somewhat technical and thus harder to understand, I'm asking for someone to write an easier to understand explanation based on examples about what 1NF, 2NF, 3NF, even 3.5NF (Boyce-Codd) mean.
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1NF: Only one value per column
2NF: All the non primary key columns in the table should depend on the entire primary key.
3NF: All the non primary key columns in the table should depend DIRECTLY on the entire primary key.
I have written an article in more detail over here
I've never had a good memory for exact wording, but in my database class I think the professor always said something like:
The data depends on the key [1NF], the whole key [2NF] and nothing but the key [3NF].
Here's a quick, admittedly butchered response, but in a sentence:
1NF : Your table is organized as an unordered set of data, and there are no repeating columns.
2NF: You don't repeat data in one column of your table because of another column.
3NF: Every column in your table relates only to your table's key -- you wouldn't have a column in a table that describes another column in your table which isn't the key.
For more detail, see wikipedia...
Source: Stackoverflow.com