Tuesday, 12 November 2013

SQL SERVER - Notes 3

19. What is View ?
       View is the additional layer of table, which will protect the table by exposing the appropriate columns to the external one.example view is like a Window of a home, through window no one can't see the whole home. through window it can allow only the particular room thats it. Views is used to expose the required column to the others

CREATE TABLE products
(
ID INT ,
PRODUCTNAME VARCHAR(50),
CATEGORY VARCHAR(20),
PRICE INT
)

SELECT * FROM dbo.products
CREATE VIEW PRO_VIEW
WITH ENCRYPTION
AS
SELECT PRODUCTNAME,PRICE FROM DBO.PRODUCTS
WITH CHECK OPTION

SELECT * FROM pro_view

Here is used to encrypt the view code so no one can see the code, in  the above code products table have four columns but in view we are exposing two columns alone.Using view we can insert , update and delete data in the table.

Following rules must be follow for insert , update and delete using view.

·         If you are using a view to insert data, then your view should have a single select and also all the mandatory columns of the “being edited” table must be included in the view unless the table has a default values for all NOT NULL columns of the table.
·         Secondly don’t forget, for views with “WITH CHECK” options enabled, it’s important to keep in mind that the data begin inserted qualifies in the WHERE clause of the view and is certain to be selected by the view. Simply put the data you insert is picked up while you select from your view.
·         If the view is having joins with more than one table, then most cases chances of modifying capabilities are negligible unless INSTEAD OF Triggers are in place to handle the request.
INSERT INTO pro_view VALUES ('WM',23000)



20 . What is Normalization ?

What is Normalization ?
  Normalization is a process of eliminating Redundant data and storing the related information in a table.


1. Eliminating Redundant data.
2. Faster update
3. Improve performance
4. Performance in indexes

Let we see different Normalization forms

1. First Normal Form (1NF)
    If a Table is said to be 1NF then it should satisfy following rules.

  • Each cell must have one value
  • Eliminating Duplicate Columns
  • Create a separate table for group of related data and each row must be identify by primary key.
That means each cell must have single value and each row should be uniquely identified by Primary key

For Example :

Name
Department
Phone Number
Rajesh
Computer
3452342,1234563,2345612
Suresh
Electronics
2398521,2323177,5302994
Praba
Civil
3958218
In the above we can see the duplicate columns phone numbers have more than one value , we have to eliminate that and create a group of related data with Unique row identification by specifying a primary key for the table

Rule 1. By applying above rule each cell must have one value above table changes like below

Name
Department
Phone Number
Phone Number
Phone Number
Rajesh
Computer
3452342
1234563
2345612
Suresh
Electronics
2398521
2323177
5302994
Praba
Civil
3958218



Rule 2 & 3 . By applying second rule and third rule no more duplicate columns and each row must be unique is applied     to above table.

Id
Name
Department
Phone Number
1
Rajesh
Computer
3452342
2
Rajesh
Computer
1234563
3
Rajesh
Computer
2345612
4
Suresh
Electronics
2398521
5
Suresh
Electronics
2323177
6
Suresh
Electronics
5302994
7
Praba
Civil
3958218


2. Second Normal Form (2NF)
    The Table must be in second normal form , Then it should satisfy the following rules.
  •  It should satisfy first normal form
  •  Separate the particular columns ,values are duplicated in each row  should be place in separate table
  •  Create the relationship between the tables
From the above table we can see the column name and department are repeated in each row ,This two columns can be maintained in another table and make a relationship between these two tables 

EmpId
Name
Department
1
Rajesh
Computer
2
Suresh
Electronics
3
Praba
Civil

Id
EmpId
PhoneNumber
1
1
3452342
2
1
1234563
3
1
2345612
4
2
2398521
5
2
2323177
6
2
5302994
7
3
3958218
In the above table Empid is played as Primary key for the first table and foreign key for the second table.



3. Third Normal Form (3NF)
     The table must be in 3NF,if it is satisfying the following rules
  •  Must be in 2NF
  •  Separate the columns that are not dependent upon the primary key of the table.
Product
Price
Tax
LED
23000
20%
AC
15000
10%
Fridge
12000
15%

From the above table you can see that Tax Column is not dependent on Product Primary key column, It is dependent on Price so we separate that in to two different table.

Product
Price
LED
23000
AC
15000
Fridge
12000

Price
Tax
23000
20%
15000
10%
12000
15%


4. Fourth Normal Form (4NF)
  • It should be in 3NF
  • The non key columns should be dependent on full primary key instead of partial key , If then separate it.
From the following table "EmployeeName" Non-Key column not dependent on full primary key "ManagerId,EmployeeId,TaskID" it depends upon the EmployeeId  Partial Key so it can be separated.


ManagerId
EmployeeId
TaskID
EmployeeName
M1
E1
T1
Rajesh
M2
E1
T1
Rajesh

ManagerId
EmployeeId
TaskID
M1
E1
T1
M2
E1
T1

EmployeeId
EmployeeName
E1
Rajesh

21. What is the difference between the SET and SELECT ?
       Click Here to Read

22. What is Indexes ?
      Indexes is used to find the records as faster, Two types of indexes are there 1. Clustered and 2. Non- Clustered

A table can only have one clustered index and many non clustered indexes

example:

CREATE CLUSTERED INDEX ind_sx ON dbo.products(ID)
CREATE NONCLUSTERED INDEX ind_nsx ON dbo.products(CATEGORY)

23. What is Joins?
       Join is nothing but Fetching records from two or more tables by combining the  two or more tables based on similar condition on a column.

Types of Join :
Inner Join       - Join between two tables
Outer Join
    Left Outer    - Left side table can have value but right side table specify null if condition fails
    Right Outer  - Right side table have full value but sets null value in left side if condition fails
    Full Outer     - Specify both side null if condition fails
Cross Join      - Each row of first table joins with the each row of second table.
Self Join          - A table join with itself

CREATE TABLE EMPLOYEE
(
id INT IDENTITY(1,1),
NAME varchar(40),
addr varchar(50)
)

CREATE TABLE EMP_LEAVE
(
id INT ,
leaveDAYS INT
)

INSERT INTO employee(name,addr) VALUES('raj','chennai')
INSERT INTO employee(name,addr) VALUES('ram','banglore')
INSERT INTO employee(name,addr) VALUES('siva','US')

INSERT INTO emp_leave(id,leavedays) VALUES(1,4)
INSERT INTO emp_leave(id,leavedays) VALUES(5,1)

SELECT e.id,e.name ,l.leavedays
FROM employee e
JOIN emp_leave l
ON e.id = l.id

SELECT e.id,e.name ,l.leavedays
FROM employee e
LEFT OUTER JOIN emp_leave l
ON e.id = l.id

SELECT e.id,e.name ,l.leavedays
FROM employee e
RIGHT OUTER JOIN emp_leave l
ON e.id = l.id

SELECT e.id,e.name ,l.leavedays
FROM employee e
CROSS JOIN emp_leave l


24. How to create a Dynamic Query and execute it ?
Query which is framed at runtime and execute is known as dynamic query.

DECLARE @dynamic NVARCHAR(100)
SELECT @dynamic = 'select * from products'
EXEC(@dynamic)


25. What is cursor and sample ?
      cursor is used to Row by row iteration of records from a table.

DECLARE @id INT
DECLARE @name VARCHAR(40)
DECLARE @category VARCHAR(50)

DECLARE cur CURSOR
FOR SELECT id,productname,category FROM dbo.products
OPEN cur
      FETCH NEXT FROM cur INTO @id, @name,@category
      WHILE @@FETCH_STATUS = 0
      BEGIN
     
      SELECT @id AS 'product id', @name AS 'Product name', @category AS 'Category'
      FETCH NEXT FROM cur INTO @id, @name,@category
     
      END
CLOSE cur
DEALLOCATE cur


26. While loop sample

DECLARE @i INT
SELECT @i = 1

WHILE @i < 8
BEGIN
PRINT @i
SELECT @i = @i +1
END


27. What is the best practices in SQL SERVER ?
       Click here to read



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