How do I normalize data in a database? - database

Question

I'm in an intro to database management course and we're learning about normalizing data (1NF, 2NF, 3NF, etc.) and I'm super confused on how to actually go about and do it. I've read up on this, consulted various sites and youtube videos and I still can't seem to get it to click. I am using Microsoft Access 2013 if that's of any help.
This is the data I'm working with.
Thanks.
Edit1: Alright, I think I have the tables set up correctly. But now I'm having trouble actually inputting data to go from one table to the next. Here's my relationship table.

Answer 1

On a very basic level, any repeating values in a table are candidates for normalization. Duplicated data is usually a bad idea. Say you needed to update a patient's surname - you now have to update all the occurrences in this table, and possibly many others throughout the rest of the database. Much better to store each patient's details in one place only.
This is where normalization comes in. Looking down the columns, you can see that there are repeating values for data about dentists, patients and surgeries, so we should normalize towards having tables for each of these entities, as well as the original table that contains appointments, giving you four tables in total.
Extract the entities out into their own tables, and give each row a primary (unique) key - just use an incrementing integer for now. (Edit: as suggested in the comment we could use the natural keys of PatientNo, StaffNo and SurgeryNo instead of creating surrogates.)
Then, instead of each patient's name and number appearing multiple times in the appointments table, we just reference the key of the master record in the Patient table. This is called a foreign key.
Then, do the same for Dentist and Surgery.
You will end up with tables looking something like this:
APPOINTMENT
AppointmentID DentistID PatientID AppointmentTime SurgeryID
----------------------------------------------------------------
1 1 1 12 Aug 03 10:00 1
2 1 2 ... 2
3 2 3 ... 1
4 2 3 ... 1
5 3 2 ... 2
6 3 4 ... 3
DENTIST
DentistID Name StaffNo
--------------------------------------
1 Tony Smith S1011
2 Helen Pearson S1024
3 Robin Plevin S1032
PATIENT
PatientID Name PatientNo
---------------------------------------
1 Gillian White P100
2 Jill Bell P105
3 Ian MackKay P108
4 John Walker P110
SURGERY
SurgeryID SurgeryNo
-------------------------
1 S10
2 S15
3 S13

Answer 2

The first step is to data modelling and denormalization is to understand your data. Study it an understand the domain "objects" or tables that exist within your model. That will give you an idea of how to start. Sometimes a single table or query sample is not enough to fully understand the database, but in your case, we can use the sample data and make some assumptions.
Secondly, look for repeated / redundant data. If you see copies of names, there is a good chance that is a candidate for a foreign key. Our assumption tells us that STAFF_NO is a primary key candidate for DENTIST because each unique STAFF_NO correlates to a unique DENTIST_NAME, so I see a good candidate DENTIST table (STAFF_NO, DENTIST_NAME)
Example in some table of SURGERY:
ID STAFF_NO DENTIST_NAME
1 1 Fred Sanford
2 1 Fred Sanford
3 3 Lamont Sanford
4 3 Lamont Sanford
Why store these over and over? What happens when Fred says "But my correct name is Fred G Sanford", so you have to update your database. In the current table, you have to update the name is many rows. If you had normalized it, you'd have a single location for the name, in the DENTIST table.
So I can take the unique dentists and store them in DENTIST
create table DENTIST(staff_no integer primary key, dentist_name varchar(100));
-- One possible way to populate our dentist table is to use a distinct query from surgery
insert into DENTIST
select distinct staff_no, dentist_name from surgery;
STAFF_NO DENTIST_NAME
1 Fred Sanford
3 Lamont Sanford
SURGERY table now points to DENTIST table
ID STAFF_NO
1 1
2 1
3 3
4 3
And you can now create a view, VIEW_SURGERY to join the DENTIST_NAME back in to satisfy the needs of typical queries.
select s.id, d.staff_no, d.dentist_name
from surgery s join dentist d
on s.staff_no = d.staff_no -- join here
So now a unique update to DENTIST, by the dentist primary key will update a single row.
update dentist set name = 'Fred G Sanford' where staff_no = 1;
Add query view will show the updated name for N rows:
select * from view_surgery
ID STAFF_NO DENTIST_NAME
1 1 Fred G Sanford
2 1 Fred G Sanford
3 3 Lamont Sanford
4 3 Lamont Sanford
In short, you are removing redundancy.
This is just a sample, and one way to do it. Manual normalization like this is not as common when you have modelling tools, but the point is, we can look at data, spot redundancies and factor those redundancies into new tables, and relate those new tables by foreign keys and joins, then build views to represent the original data.