Hello World! I'm talking about creating normalized tables.

If there are no repeating

fields, where does that information go?

Here's an example:

We have an ID and name and birthday for friends.

And then we realized that we have multiple phone numbers

for some of our friends.

If we can't have repeating

fields,

Where do we put the phone numbers?

We need another table.

If you look at this, you can see that

Ann Rogers is ID 1.

And we have three phone numbers for her.

We have a cell phone, a home phone, and an office phone.

And then for Carl Jones we have just a cell phone.

The key for the table of our friends

is an ID that might be Auto generated number.

For this table with the phone numbers, we have a

combination key.

Because we need both the ID and the phone number to

uniquely identify that.

The reason we need both keys

Is because more than one person

Could have the same phone number. That's especially true

with home phone numbers and office numbers.

So we need a

combination key.

Here's another example:

We have courses, very simplified, and we have students.

We could have zero to many students, 0:M in a course.

And a student could be taking 0 to many, 0:M courses.

We add a table: let's call this registration.

And we can see from this that student Amy Rogers.

Is taking math,

And

Amy Rogers

is also taking English.

Rick Smith is taking math.

With this arranged this way we could easily list all the

students in a course.

For instance, we could select

all

records that have M1,

and print out a class list. And we could select all of the

records that have the student ID 2409

to print out Amy Rogers schedule of classes.

The key for the course is the ID.

The key for the student table is the

Student ID.

But for this table we have the combination key: the ID for

the course and the student ID.

Another rule in normalization is that all fields must depend on the keys.

For this table with the friends, the ID is

Simply their number.

We could add fields here about that person.

For instance, we might give their address.

For this because, we have the combination field, we can only add fields.

That depend on both the ID, the person, and the phone number.

So we could add fields such as.

When this was updated, when

that person's phone number was updated in this table.

For the course table,

the fields would have to pretend to this one ID.

So we could add the title of the course, the number of credits,

Information like that.

For the student table we could

add information about that student for instance their

birthday or their major.

Information like that about the student.

For this table,

because we have the combination key,

we could only add information about that student, and

that course. So that could be information such as

they registered, whether it's for audit or credit, or even the

grade they got in that course.

And that's it.