Normalization

Building Database Relationships

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Normalization

You’ve been creating tables without giving much thought to them. And that’s fine, they work. You can SELECT,INSERT, DELETE, and UPDATE with them.

As you get more data, you start seeing things you wish you’d done to make your WHERE clauses simpler.

What you need is to make your tables more normal.

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Steps to Normalization

Making your data atomic First Normal Form – 1NF

Each row of data must contain atomic values. Each row of data must have a unique identifier, known as

a Primary Key. (To make our tables completely normal, we need to give each record a Primary Key.)

There is a 2NF and 3NF, that we will get to in the near future.

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All about relationships

1. Pick your thing, the one thing you want your table to describe. (What’s the main thing you want your table to be about?)

2. Make a list of the information you need to know about your one thing when you’re using the table. (How will you use this table?)

3. Using the list, break down the information about your thing into pieces you can use for organizing your table. (How can you most easily query this table?)

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Atomic Data

Atomic data has been broken down into the smallest pieces of data that can’t or shouldn’t be divided any further.

Consider a pizza delivery guy. To get to where he’s going, he just needs a street number and address in a single column. For his purposes, that’s atomic. He never needs to look for a single street number on its own.

In fact, if his data were broken into street number and street name, his queries would have to be longer and more complicated, making it take him longer to get the pizza to your front door.

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Atomic Data

Now consider a realtor. He might want to have a separate columns for the street number. He may want to query on a given street to see all the houses for sale by street number.

For him, street number and street name are each atomic.

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The Benefits of Normal Tables

Normal tables won’t have duplicate data, which will reduce the size of your database.

With less data to search through, your queries will be faster.

If you begin with a normalized table, you won’t have to go back and change your table when your queries go too slowly.

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Remember that Clown Table?

Clown tracking has become a nationwide craze, and our old table isn't going to cut it because the appearance and activities columns contain so much data. For our purposes, this table is not atomic.

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First Normal Form – 1NF

To be 1NF, a table must follow these two rules:

Each row of data must contain atomic values.

Each row of data must have a unique identifier, known as a Primary Key. (To make our tables completely normal, we need to give each record a Primary Key.)

There is a 2NF and 3NF, that we will get to in the near future.

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PRIMARY KEY rules

A primary key is a column in your table that makes each record unique.

The column in your table that will be your primary key has to be designated as such when you create the table.

Which means that the data in the primary key column can’t be repeated.

Consider a table with the columns shown below. Do you think any of those would make good primary keys?

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PRIMARY KEY rules

A primary key can’t be NULL. If it's null, it can't be unique because other records can also be NULL.

The primary key must be given a value when the record is inserted. When you insert a record without a primary key, you run the risk of ending up with a NULL primary key and duplicate rows in your table, which violates First Normal Form.

The primary key must be compact. A primary key should contain only the information it needs to to be unique and nothing extra.

The primary key values can’t be changed. If you could change the value of your key, you’d risk accidentally setting it to a value you already used. Remember, it has to remain unique.

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Primary Key Exercise

Table 1 –Airline Flight number Destination Depart_From Depart_Time Arrival_Time Aircraft_Type

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Primary Key Exercise

Table 2 –Student Name Address City State Zip Phone# SS#

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Primary Key Exercise

Table 3 –ZooAnimals Type Name Gender B_Day Tag Number

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Take care using SSNs as the Primary Keys for your records. With identity theft only increasing, people don’t

want to give out SSNs— and with good reason. They’re too important to risk.

Can you absolutely guarantee that your database is secure?

If it’s not, all those SSNs can be stolen, along with your customers’ identities.

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The best primary key may be a new primary key. When it comes to creating primary keys, your best

bet may be to create a column that contains a unique number.

Think of a table with people’s info, but with an additional column containing a number. Let’s think of it as id.

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Geek Bits

There's a big debate in the SQL world about using synthetic, or made-up, primary keys (like the ID column above) versus using natural keys—data that is already in the table (like a VIN number on a car or SSN number).

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Getting to Normal

Creating a primary key is normally something we do when we write our CREATE TABLE code.

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Let’s look at Greg’s table my_contacts

It’s not atomic and it has no primary key. From what you’ve seen so far, this is how you’d

have to fix Greg’s table:

Step 1: SELECT all of your data and save it somehow.

Step 2: Create a new normal table.

Step 3: INSERT all that old data into the new table, changing each row to match the new table structure.

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Let’s look at Greg’s table my_contacts

So now you can drop your old table. NO! We can add a primary key to Greg’s table and

make the columns more atomic using just one new command.

Let’s look at our original commands:

CREATE TABLE my_contacts

(

last_name VARCHAR(30),

first_name VARCHAR(20),

email VARCHAR(50),

gender CHAR(1),

birthday DATE,

profession VARCHAR(50),

location VARCHAR(50),

status VARCHAR(20),

interests VARCHAR(100),

seeking VARCHAR(100)

);

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CREATE TABLE with PRIMARY KEY

At the top of the column list we added a contact_id column that we’re setting to NOT NULL, and at the bottom of the list, we’re add a line PRIMARY KEY, which we set to use our new contact_id column as the primary key.

CREATE TABLE my_contacts

(

contact_id INT NOT NULL,

last_name varchar(30) default NULL,

first_name varchar(20) default NULL,

email varchar(50) default NULL,

gender char(1) default NULL,

birthday date default NULL,

profession varchar(50) default NULL,

location varchar(50) default NULL,

status varchar(20) default NULL,

interests varchar(100) default NULL,

seeking varchar(100) default NULL,

PRIMARY KEY (contact_id)

)

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Auto Increment

AUTO_INCREMENT When used in your column declaration, that column will automatically be given a unique integer value each time an INSERT command is performed.

Adding the keyword AUTO_INCREMENT to our contact_id column makes our SQL software automatically fill that column with a value that starts on row 1 with a value of 1 and goes up in increments of 1

CREATE TABLE my_contacts

(

contact_id INT NOT NULL AUTO_INCREMENT,

last_name varchar(30) default NULL,

…

…

…

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Adding the PK to an existing table

Here’s the code to add an AUTO_INCREMENT primary key to Greg’s my_contacts table.

ALTER TABLE my_contacts

ADD COLUMN contact_id INT NOT NULL AUTO_INCREMENT FIRST,

ADD PRIMARY KEY (contact_id);

Our new SQL command, ALTER ADD COLUMN does just that. It says to add a

column to the table and name it contact_id. FIRST tells the software to make the new column

the first one in the list. This is optional, but it’s good form to put your primary key first.

Let’s try this!

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To see what happened to your table:

SELECT * from my_contacts; The contact_id column has been added first in the

table before all the other columns. Because we used AUTO_INCREMENT, the

column was filled in as each record in the table was updated

The next time we INSERT a new record, the contact_id column will be given a value one higher than the highest contact_id in the table. If the last record has a contact_id of 23, the next one will be 24.

Let’s add a new record!

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Questions???