PHP mysql Database normalizatin

Database NormalizationDatabase Normalization

What is NormalizationWhat is Normalization
 Normalization allows us to organize
data so that it:
• Allows faster access (dependencies
make sense)
• Reduced space (less redundancy)

Normal FormsNormal Forms
 Normalization is done through
changing or transforming data into
various Normal Forms.
 There are 5 Normal Forms but we
almost never use 4NF or 5NF.
 We will only be concerned with 1NF,
2NF, and 3NF.

 For a database to be in a normal
form, it must meet all requirements
of the previous forms:
• Eg. For a database to be in 2NF, it must
already be in 1NF. For a database to be
in 3NF, it must already be in 1NF and
2NF.

Sample DataSample Data
Manager Employees
Fatma Sayed, Tariq
Abdulaziz Tafla, Mohammed
Ali Sarai, Miriam
 This data has some problems:
• The Employees column is not atomic.
 A column must be atomic, meaning that it
can only hold a single item of data. This
column holds more than one employee
name.

Manager Employees
Fatma Sayed, Tariq
Abdulkaziz Tafla, Mohammed
Ali Sarai, Miriam
 Data that is not atomic means:
• We can’t easily sort the data
• We can’t easily search or index the data
• We can’t easily change the data
• We can’t easily reference the data in
other tables

Manager Employee1 Employee2
Fatma Sayed Tariq
Abdulaziz Tafla Mohammed
Ali Sarai Miriam
 Breaking the Employee column into
more than 1 column doesn’t solve
our problems:
• The data may look atomic, but only
because we have many identical
columns storing a single piece of data
instead of a single column storing many
pieces of data.

• We still can’t easily sort, search, or
index our employees.
• What if a manager has more than 2
employees, 10 employees, 100
employees? We’d need to add columns
to our database just for these cases.
• It is still hard to reference our
employees in other tables.

Manager Employee1 Employee2
Fatma Sayed Tariq
Abdulaziz Tafla Mohammed
Ali Sarai Miriam
 By the way, what would be a good
choice of a Primary Key for this
table?

First Normal FormFirst Normal Form
 1NF means that we must:
• Eliminate duplicate columns from the
same table, and
 Let’s get started by making our
columns atomic…

Atomic DataAtomic Data
 By breaking each
tuple of our table
into an entry for
each employee, we
have made our
data atomic.
 What would be the
primary key?
Manager Employee
Fatma Sayed
Fatma Tariq
Abdulaziz Tafla
Abdulaziz Mohammed
Ali Sarai
Ali Miriam

Primary KeyPrimary Key
 The best primary
key would be the
Employee column.
 Every employee
only has one
manager, therefore
an employee is
unique.
Employee Manager
Sayed Fatma
Tariq Fatma
Tafla Abdulaziz
Mohammed Abdulaziz
Sarai Ali
Miriam Ali

First Normal FormFirst Normal Form
 Congratulations!
 The fact that all
our data and
columns is atomic
and we have a
primary key means
that we are in 1NF!
Employee Manager
Sayed Fatma
Tariq Fatma
Tafla Abdulaziz
Mohammed Abdulaziz
Sarai Ali
Miriam Ali

First Normal Form RevisedFirst Normal Form Revised
 Of course there
may come a day
when we hire a
second employee
or manager with
the same name. To
avoid this, let’s use
an employee ID
instead of their
name.
ID Employee ManagerID
1 Sayed 7
2 Tariq 7
3 Tafla 8
4 Mohammed 8
5 Sarai 9
6 Miriam 9
7 Fatma
8 Abdulaziz
9 Ali

1NF: Before and After1NF: Before and After
ID Employee ManagerID
1 Sayed 7
2 Tariq 7
3 Tafla 8
4 Mohammed 8
5 Sarai 9
6 Miriam 9
7 Fatma
8 Abdulaziz
9 Ali
Manager Employees
Fatma Sayed, Tariq
Abdulaziz Tafla, Mohammed
Ali Sarai, Miriam

Moving to Second Normal FormMoving to Second Normal Form
 A database in 2NF must also be in
1NF:
• Data must be atomic
• Every row (or tuple) must have a unique
primary key
 Plus:
• Subsets of data that apply to multiple
rows (repeating data) are moved to
separate tables

CustID FirstName LastName Address City State Zip
1 Bob Smith 123 Main St. Tucson AZ 12345
2 John Brown 555 2nd Ave. St. Paul MN 54355
3 Sandy Jessop 4256 James St. Chicago IL 43555
4 Maria Hernandez 4599 Columbia Vancouver BC V5N 1M0
5 Gameil Hintz 569 Summit St. St. Paul MN 54355
6 James Richardson 12 Cameron Bay Regina SK S4T 2V8
7 Shiela Green 12 Michigan Ave. Chicago IL 43555
8 Ian Sampson 56 Manitoba St. Winnipeg MB M5W 9N7
9 Ed Rodgers 15 Athol St. Regina SK S4T 2V9
This data is in 1NF: all fields are atomic and the CustID serves as
the primary key

 But let’s pay
attention to the
City, State, and Zip
fields:
• There are 2 rows of
repeating data:
one for Chicago,
and one for St.
Paul.
• Both have the same
city, state and zip
code
City State Zip
Tucson AZ 12345
St. Paul MN 54355
Chicago IL 43555
Vancouver BC V5N 1M0
St. Paul MN 54355
Regina SK S4T 2V8
Chicago IL 43555
Winnipeg MB M5W 9N7
Regina SK S4T 2V9

 The CustID determines all the data in the
row, but U.S. Zip codes determines the
City and State. (eg. A given Zip code can
only belong to one city and state so
storing Zip codes with a City and State is
redundant)
 This means that City and State are
Functionally Dependent on the value in
Zip code and not only the primary key.

 To be in 2NF, this repeating data
must be in its own table.
 So:
• Let’s create a Zip code table that maps
Zip codes to their City and State.

Our Data in 2NFOur Data in 2NF
CustID FirstName LastName Address Zip
1 Bob Smith 123 Main St. 12345
2 John Brown 555 2nd Ave. 54355
3 Sandy Jessop 4256 James St. 43555
4 Maria Hernandez 4599 Columbia V5N 1M0
5 Gameil Hintz 569 Summit St. 54355
6 James Richardson 12 Cameron Bay S4T 2V8
7 Shiela Green 12 Michigan Ave. 43555
8 Ian Sampson 56 Manitoba St. M5W 9N7
9 Ed Rodgers 15 Athol St. S4T 2V9
Zip City State
12345 Tucson AZ
54355 St. Paul MN
43555 Chicago IL
V5N 1M0 Vancouver BC
S4T 2V8 Regina SK
M5W 9N7 Winnipeg MB
S4T 2V9 Regina SK
•We see that we can actually save 2
rows in the Zip Code table by removing
these redundancies: 9 customer
records only need 7 Zip code records.
•Zip code becomes a foreign key in the
customer table linked to the primary
key in the Zip code table
CustomerTableZipCodeTable

Advantages of 2NFAdvantages of 2NF
 Saves space in the database by
reducing redundancies
 If a customer calls, you can just ask
them for their Zip code and you’ll
know their city and state! (No more
spelling mistakes)
 If a City name changes, we only
need to make one change to the
database.

Summary So Far…Summary So Far…
 1NF:
• All data is atomic
• All rows have a unique primary key
 2NF:
• Data is in 1NF
• Subsets of data in multiple columns are
moved to a new table
• These new tables are related using
foreign keys

Moving to 3NFMoving to 3NF
 To be in 3NF, a database must be:
• In 2NF
• All columns must be fully functionally
dependent on the primary key (There
are no transitive dependencies)

 In this table:
• CustomerID and ProdID depend on the
OrderID and no other column (good)
• Stated another way, “If you know the OrderID,
you know the CustID and the ProdID”
 So: OrderID  CustID, ProdID
OrderID CustID ProdID Price Quantity Total
1 1001 AB-111 50 1,000 50,000
2 1002 AB-111 60 500 30,000
3 1001 ZA-245 35 100 3,500
4 1003 MB-153 82 25 2,050
5 1004 ZA-245 42 10 420
6 1002 ZA-245 40 50 2,000
7 1001 AB-111 75 100 7,500

 But there are some fields that are
not dependent on OrderID:
• Total is the simple product of
Price*Quantity. As such, has a transitive
dependency to Price and Quantity.
• Because it is a calculated value, doesn’t
need to be included at all.
1 1001 AB-111 50 1,000 50,000
2 1002 AB-111 60 500 30,000
3 1001 ZA-245 35 100 3,500
4 1003 MB-153 82 25 2,050
5 1004 ZA-245 42 10 420
6 1002 ZA-245 40 50 2,000
7 1001 AB-111 75 100 7,500

 Also, we can see that Price isn’t
really dependent on ProdID, or
OrderID. Customer 1001 bought AB-
111 for $50 (in order 1) and for $75
(in order 7), while 1002 spent $60
for each item in order 2.
1 1001 AB-111 50 1,000 50,000
2 1002 AB-111 60 500 30,000
3 1001 ZA-245 35 100 3,500
4 1003 MB-153 82 25 2,050
5 1004 ZA-245 42 10 420
6 1002 ZA-245 40 50 2,000
7 1001 AB-111 75 100 7,500

 Maybe price is dependent on the
ProdID and Quantity: The more you
buy of a given product the cheaper
that product becomes!
 So we ask the business manager and
she tells us that this is the case.
1 1001 AB-111 50 1,000 50,000
2 1002 AB-111 60 500 30,000
3 1001 ZA-245 35 100 3,500
4 1003 MB-153 82 25 2,050
5 1004 ZA-245 42 10 420
6 1002 ZA-245 40 50 2,000
7 1001 AB-111 75 100 7,500

 We say that Price has a transitive
dependency on ProdID and Quantity.
• This means that Price isn’t just determined by
the OrderID. It is also determined by the size
(or quantity) of the order (and of course what
is ordered).
1 1001 AB-111 50 1,000 50,000
2 1002 AB-111 60 500 30,000
3 1001 ZA-245 35 100 3,500
4 1003 MB-153 82 25 2,050
5 1004 ZA-245 42 10 420
6 1002 ZA-245 40 50 2,000
7 1001 AB-111 75 100 7,500

 Let’s diagram the dependencies.
 We can see that all fields are
dependent on OrderID, the Primary
Key (white lines)

 But Total is also determined by Price
and Quantity (yellow lines)
• This is a derived field
(Price x Quantity = Total)
• We can save a lot of space by getting rid
of it altogether and just calculating total
when we need it

 Price is also determined by both
ProdID and Quantity rather than the
primary key (red lines). This is called
a transitive dependency. We must
get rid of transitive dependencies to
have 3NF.
OrderID CustID ProdID Price Quantity

 We do this by moving the transitive
dependency into a second table…
OrderID CustID ProdID Price Quantity

 By splitting out the
table, we can
quickly adjust our
price table to meet
our competitor, or
if the prices
changes from our
suppliers.
OrderID CustID ProdID Quantity
ProdID PriceQuantity

 The second table is our pricing list.
 Think of Quantity as a range:
• AB-111: 1-100, 101-500, 501 and more
ZA-245: 1-10, 11-50, 51 and more
 The primary Key for this second table is a
composite of ProdID and Quantity.
OrderID CustID ProdID Quantity ProdID Quantity Price
1 1001 AB-111 1,000 AB-111 1 75
2 1002 AB-111 500 AB-111 101 60
3 1001 ZA-245 100 AB-111 501 50
4 1003 MB-153 25 ZA-245 1 42
5 1004 ZA-245 10 ZA-245 11 40
6 1002 ZA-245 50 ZA-245 51 35
7 1001 AB-111 100 MB-153 1 82

 Congratulations! We’re now in 3NF!
 We can also quickly figure out what
price to offer our customers for any
quantity they want.
OrderID CustID ProdID Quantity ProdID Quantity Price
1 1001 AB-111 1,000 AB-111 1 75
2 1002 AB-111 500 AB-111 101 60
3 1001 ZA-245 100 AB-111 501 50
4 1003 MB-153 25 ZA-245 1 42
5 1004 ZA-245 10 ZA-245 11 40
6 1002 ZA-245 50 ZA-245 51 35
7 1001 AB-111 100 MB-153 1 82

To Summarize (again)To Summarize (again)
 A database is in 3NF if:
• It is in 2NF
• It has no transitive dependencies
 A transitive dependency exists when one
attribute (or field) is determined by another
non-key attribute (or field)
 We remove fields with a transitive
dependency to a new table and link them by
a foreign key.

SummarizingSummarizing
• It is in 1NF
• There is no repeating data in its tables.
 Put another way, if we use a composite
primary key, then all attributes are
dependent on all parts of the key.

And Finally…And Finally…
• All its attributes are atomic (meaning
they contain only a single unit or type of
data), and
• All rows have a unique primary key.

PHP mysql Database normalizatin

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