OVER ( 
       [ <PARTITION BY clause> ]
       [ <ORDER BY clause> ] 
       [ <ROW or RANGE clause> ]
      )

<PARTITION BY clause> ::=
PARTITION BY value_expression , ... [ n ]

<ORDER BY clause> ::=
ORDER BY order_by_expression
    [ COLLATE collation_name ] 
    [ ASC | DESC ] 
    [ ,...n ]

<ROW or RANGE clause> ::=
{ ROWS | RANGE } <window frame extent>

<window frame extent> ::= 
{   <window frame preceding>
  | <window frame between>
}

<window frame between> ::= 
  BETWEEN <window frame bound> AND <window frame bound>

<window frame bound> ::= 
{   <window frame preceding>
  | <window frame following>
}

<window frame preceding> ::= 
{
    UNBOUNDED PRECEDING
  | <unsigned_value_specification> PRECEDING
  | CURRENT ROW
}

<window frame following> ::= 
{
    UNBOUNDED FOLLOWING
  | <unsigned_value_specification> FOLLOWING
  | CURRENT ROW
}

<unsigned value specification> ::= 
{  <unsigned integer literal> }

CREATE TABLE REVENUE
(
[DepartmentID] int,
[Revenue] int,
[Year] int
);
 
insert into REVENUE
values (1,10030,1998),(2,20000,1998),(3,40000,1998),
 (1,20000,1999),(2,60000,1999),(3,50000,1999),
 (1,40000,2000),(2,40000,2000),(3,60000,2000),
 (1,30000,2001),(2,30000,2001),(3,70000,2001)
 

 select *,
 avg(Revenue) OVER (PARTITION by DepartmentID) as AverageRevenue,
 sum(Revenue) OVER (PARTITION by DepartmentID) as TotalRevenue
from REVENUE
order by departmentID, year;

 insert into REVENUE
 values(1,90000,2002),(2,20000,2002),(3,80000,2002),
 (1,10300,2003),(2,1000,2003), (3,90000,2003),
 (1,10000,2004),(2,10000,2004),(3,10000,2004),
 (1,20000,2005),(2,20000,2005),(3,20000,2005),
 (1,40000,2006),(2,30000,2006),(3,30000,2006),
 (1,70000,2007),(2,40000,2007),(3,40000,2007),
 (1,50000,2008),(2,50000,2008),(3,50000,2008),
 (1,20000,2009),(2,60000,2009),(3,60000,2009),
 (1,30000,2010),(2,70000,2010),(3,70000,2010),
 (1,80000,2011),(2,80000,2011),(3,80000,2011),
 (1,10000,2012),(2,90000,2012),(3,90000,2012)

select Year, DepartmentID, Revenue,
sum(Revenue) OVER (PARTITION by DepartmentID ORDER BY [YEAR]
             ROWS BETWEEN 3 PRECEDING AND CURRENT ROW) as Prev3
From REVENUE order by departmentID, year;

ROWS BETWEEN 3 PRECEDING AND CURRENT ROW) as Prev3

select Year, DepartmentID, Revenue,
 sum(Revenue) OVER (PARTITION by DepartmentID ORDER BY [YEAR]
              ROWS BETWEEN CURRENT ROW AND 3 FOLLOWING) as Next3
From REVENUE order by departmentID, year;

select Year, DepartmentID, Revenue,
       min(Revenue) OVER (PARTITION by DepartmentID ORDER BY [YEAR]
                    ROWS UNBOUNDED PRECEDING) as MinRevenueToDate
From REVENUE order by departmentID, year;

RANGE UNBOUNDED PRECEDING AND CURRENT ROW 

CREATE TABLE Employees (  
    EmployeeId INT IDENTITY PRIMARY KEY,  
    Name VARCHAR(50),  
    HireDate DATE NOT NULL,  
    Salary INT NOT NULL  
)  
GO  
INSERT INTO Employees (Name, HireDate, Salary)  
VALUES   
    ('Alice', '2011-01-01', 20000),  
    ('Brent', '2011-01-15', 19000),  
    ('Carlos', '2011-02-01', 22000),  
    ('Donna', '2011-03-01', 25000),  
    ('Evan', '2011-04-01', 18500)  
GO  

SELECT  
    Name,   
    Salary,   
    AVG(Salary) OVER(ORDER BY HireDate) AS avgSalary  
FROM Employees  
GO 

SELECT  
    Name,   
    Salary,   
    AVG(Salary) OVER(ORDER BY HireDate 
                 RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS avgSalary  
FROM Employees  
GO

SELECT  
    Name,   
    Salary,   
    AVG(Salary) OVER(ORDER BY HireDate   
                        RANGE   
                        BETWEEN UNBOUNDED PRECEDING   
                        AND UNBOUNDED FOLLOWING  
                    ) AS avgSalary  
FROM Employees  
GO