Wednesday, July 5, 2017

Normalization in SQL Server

  July 05, 2017    

Normalization is the process of efficiently organizing data in a database. 
There are two goals of the normalization process: 
  • Eliminating redundant data (for example, storing the same data in more than one table) 
  • Ensuring data dependencies make sense (only storing related data in a table).

    Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored. There are several benefits for using Normalization in Database.
Benefits :

  1. Eliminate data redundancy
  2. Improve performance
  3. Query optimization
  4. Faster update due to less number of columns in one table
  5. Index improvement
There are different types of Normalizations form available in the Database. Lets see one by one.

1. First Normal Form (1NF)
 First normal form (1NF) sets the very basic rules for an organized database:
  • Eliminate duplicative columns from the same table.
  • Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).
    • Remove repetative groups
    • Create Primary Key

Name State Country Phone1 Phone2 Phone3
John 101 1 488-511-3258 781-896-9897 425-983-9812
Bob 102 1 861-856-6987
Rob 201 2 587-963-8425 425-698-9684
 PK

                 [ Phone Nos ]
   ?


?
ID Name State Country Phone
1 John 101 1 488-511-3258
2 John 101 1 781-896-9897
3 John 101 1 425-983-9812
4 Bob 102 1 861-856-6987
5 Rob 201 2 587-963-8425
6 Rob 201 2 425-698-9684

2. Second Normal Form (2NF)

 Second normal form (2NF) further addresses the concept of removing duplicative data:
·         Meet all the requirements of the first normal form.
·         Remove subsets of data that apply to multiple rows of a table and place them in separate tables.
·         Create relationships between these new tables and their predecessors through the use of foreign keys.   
Remove columns which create duplicate data in a table and related a new table with Primary Key – Foreign Key relationship

ID Name State Country Phone


1 John 101 1 488-511-3258


2 John 101 1 781-896-9897


3 John 101 1 425-983-9812


4 Bob 102 1 861-856-6987


5 Rob 201 2 587-963-8425


6 Rob 201 2 425-698-9684


















ID Name State Country
PhoneID ID Phone
1 John 101
1 1 488-511-3258
2 Bob 102
2 1 781-896-9897
3 Rob 201
3 1 425-983-9812



4 2 587-963-8425



5 3 587-963-8425



6 3 425-698-9684

3. Third Normal Form (3NF)
Third normal form (3NF) goes one large step further:
·         Meet all the requirements of the second normal form.
·         Remove columns that are not dependent upon the primary key.
  Country can be derived from State also… so removing country

  ID   Name   State   Country
  1   John    101       1
  2   Bob    102       1
  3   Rob    201       2

4. Fourth Normal Form (4NF)
Finally, fourth normal form (4NF) has one additional requirement:
·         Meet all the requirements of the third normal form.
·         A relation is in 4NF if it has no multi-valued dependencies.


If PK is composed of multiple columns then all non-key attributes should be derived from FULL PK only. If some non-key attribute can be derived from partial PK then remove it


The 4NF also known as BCNF NF

   TeacherID StudentID SubjectID  StudentName
     101   1001   1   John
     101   1002   2   Rob
     201   1002   3   Bob
     201   1001   2   Rob






   TeacherID    StudentID   SubjectID   StudentName
  101   1001   1          X
  101   1002   2          X
  201   1001   3          X
  201   1002   2         X

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MySQL to SQL Server Data Migration

  July 05, 2017    

For the mgiration we will use the SQL Server Import and Export Wizard.  Follow the steps below to migrate your data from a MySQL database to a SQL Server database.

  • Download and install the MySQL ODBC Connector. The latest release is available at  http://dev.mysql.com/downloads/connector/odbc/
  • Open your ODBC Data Source Administrator from the Control Panel -> Administrative Tools. On the System DSN tab click 'Add', browse the 'MySQL ODBC driver' and click 'Finish'.
     




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Tuesday, July 4, 2017

Common Table Expression (CTE)

  July 04, 2017    

 Common Table Expression (CTE) is a temporary named result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement. You can also use a CTE in a CREATE VIEW statement.
Complex SQL statements can be made easier to understand and maintainable in the form of CTE. CTE allows you to define the subquery at once, name it using an alias and later call the same data using the alias just like what you do with a normal table. CTE is standard ANSI SQL standard. 

CTE has supports two types of CTEs-recursive and nonrecursive 

 Nonrecursive:
A nonrecursive CTE is one that does not reference itself within the CTE.

EX:
WITH  cteEmployee
  AS
  (
    SELECT Id,Name,DepartmentID
    FROM employee WHERE Name LIKE 'mark%'
  )
SELECT e.Id,e.name,d.name  
FROM cteEmployee e  
INNER JOIN Department d
ON e.DepartmentID=d.ID
Recursive:
A recursive CTE is a CTE that references itself.  In doing so, the initial CTE is repeatedly executed, returning subsets of data, until the complete result is returned.


EX:

WITH   cte
AS     (SELECT 1 AS 
        UNION ALL
        SELECT n + 1 
        FROM   cte
        WHERE  n < 10 
       )
SELECT n
FROM   cte;
 
 
 

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Monday, July 3, 2017

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