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SQL etc

Posted Mar 22, 2002

Database Normalization - Page 4

By Ian Gilfillan


Let's run again through the example we've just done, this time without the data tables to guide us. After all, when you're designing a system, you usually won't have test data available at this stage. The tables were there to show you the consequences of storing data in unnormalized tables, but without them we can focus on dependency issues, which is the key to database normalization.

In the beginning, the data structure we had was as follows:

Project number
Project name
1-n Employee numbers (1-n indicates that there are many occurrences of this field - it is a repeating group)
1-n Employee names
1-n Rate categories
1-n Hourly rates

So, to begin the normalization process, we start by moving from zero normal form to 1st normal form.

The definition of 1st normal form
there are no repeating groups
all the key attributes are defined
all attributes are dependent on the primary key

So far, we have no keys, and there are repeating groups. So we remove the repeating groups, and define the primary key, and are left with the following:

Employee project table

Project number - primary key
Project name
Employee number - primary key
Employee name
Rate category
Hourly rate

This table is in 1st normal form.


Database Normalization: Part 5


 » See All Articles by Columnist Ian Gilfillan



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