Explicit and Inline Window Clauses

SQL OLAP provides two ways of specifying a window in a query:

The explicit window clause lets you define a window that follows a HAVING clause. You reference windows defined with those window clauses by specifying their names when you invoke an OLAP function, such as:
```
SUM ( ...) OVER w2
```
The inline window specification lets you define a window in the SELECT list of a query expression. This capability lets you define your windows in a window clause that follows the HAVING clause and then reference them by name from your window function invocations, or to define them along with the function invocations.

Note: If you use an inline window specification, you cannot name the window. Two or more window function invocations in a single SELECT list that use identical windows must either reference a named window defined in a window clause or they must define their inline windows redundantly.

Window function example—The following example shows a window function. The query returns a result set that partitions the data by department and then provides a cumulative summary of employees’ salaries, starting with the employee who has been at the company the longest. The result set includes only those employees who reside in Massachusetts. The column sum_salary provides the cumulative total of employees’ salaries.

SELECT DepartmentID, Surname, StartDate, Salary, SUM(Salary) OVER 
(PARTITION BY DepartmentID ORDER BY startdate 
rows between unbounded preceding and current row) 
AS sum_salary FROM Employees 
WHERE State IN ('CA') AND DepartmentID IN (100, 200)
ORDER BY DepartmentID;

The following result set is partitioned by department.

DepartmentID  Surname   start_date  salary     sum_salary
------------  --------  ----------  ---------  ----------
200           Overbey   1987-02-19  39300.000   39300.000
200           Savarino  1989-11-07  72300.000  111600.000
200           Clark     1990-07-21  45000.000  156600.000