Oct 14, 2013

Row_Number in SQL Server

Row_Number (window function) was introduced in SQL Server 2005.

Row_Number generates a run-time column in the result set which generates sequential number to each row according to the column used in order by clause.

Syntax
Row_Number() over (order by col1, col2, ....n partition by col1, col2, ....n)
  • Order By is mandatory. Row Number is assigned in the result set based on the column provided in Order By clause.
  • Partition By is optional which groups the result set based on the column provided in Partition By clause wherein each group, the sequence starts with 1.
Let's create an Employee table on which we would see how it works.
create table tblEmployee(
    EmpId char(7)
    , FirstName varchar(50)
    , LastName varchar(50)
    , Gender char(1)
)

insert into tblEmployee
select 'EMP0001', 'Sandeep', 'Mittal', 'M' union all
select 'EMP0003', 'Abhay', 'Kumar', 'M' union all
select 'EMP0005', 'Priya', 'Gupta', 'F' union all
select 'EMP0002', 'Reema', 'Gupta', 'F' union all
select 'EMP0004', 'Ritesh', 'Kumar', 'M'

Now, we would generate a sequential number for all the employees using Row_Number.
select  EmpId, FirstName, LastName, Gender
        , row_number() over (order by EmpId) as RowNum
from    tblEmployee
OUTPUT
Row Number Order By EmpId

Check out the result set where RowNum is generated based on EmpId as provided in Order By.

Multiple columns can be used in the Order By clause.

Let's take an another example where we would use multiple columns in Order By clause.
select  EmpId, FirstName, LastName, Gender
        , row_number() over (order by FirstName, LastName) as RowNum
from    tblEmployee
OUTPUT
Row Number Order By Emp Name

In the next example, we will see how Partition By clause works
select  EmpId, FirstName, LastName, Gender
        , row_number() over (partition by Gender order by EmpId) as RowNum
from    tblEmployee
OUTPUT
Row Number with Partition By Gender Order By Emp Name

Check out the result set where RowNum is generated starting from 1 for each group i.e. Gender which is provided in Partition By clause

In Partition By clause also, we can use multiple columns as in Order By clause

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