Sunday, 30 March 2014

Ranking Functions in SQL Server with example

There are four types of Ranking Functions in SQL. All the Ranking Functions are used with Over Clause
  • Row_Number: The row_number function gives each a row in a table a serial number. 
Example: 

Consider below Table named 'EmpDetails', the table contains two columns 'EmpID' and 'EmpName'
  

Now we will implement Row_number to the above table:

Query:

select *, ROW_NUMBER() over (order by empid) as Rowno from dbo.EmpDetails 

The output of the query is as follows:


  • Rank: The Rank function gives rank to each rows in the result based on the over clause.

Example:
select *, Rank() over (order by empid) as Rowno from dbo.EmpDetails 

Ouput:

As seen above, the employees with empid as '1' has been given Rank 1, whereas the employee with empid '2' has rank 3, because there were two employees with empid 1 that has rank one.


  • Dense_Rank: This function is similar to Rank() function, the only difference is that it gives Rank without any gaps.
Example:



select *, dense_Rank() over (order by empid) as Rowno from dbo.EmpDetails 

Output:

If you observe the above result set, dense_rank() function has assigned rank 2 to the employees with Empid 2, unlike Rank() function which ranked them as 3.

  • Ntile: The Ntile function requires to specify a number in the parentheses and based on that the it divides the rows in the result set.
Example:


select *, Ntile(2) over (order by empid) as Rowno from dbo.EmpDetails 

Here, we have specified 2 in the parentheses, hence the result set with contain only two ranks i.e. 1 and 2

Output:

  




1 comment:

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