Doubt regarding avoiding group by function

Question

i just came to know about a query which will avoid group by function,
select sum(column_name) over ( partition by <coulmns> order by <solumns> )
from <table_name>
now columns specified in the partition by clause, are the one which will be specified under group by clause, i know this works, but can anyone expalain the meaning and significance of over keyword and is it a function, i mean with respect to SQL language that syntax seems to be very much different isn't it???
cheere

Answer 1

Hi
Analytic functions are not alternative for group by.
Analytic functions are the last set of operations performed in a query except for the
final ORDER BY clause. All joins and all WHERE, GROUP BY, and HAVING clauses are completed before the analytic functions are processed. Therefore, analytic functions can appear only in the select list or ORDER BY clause.
And regarding your question,
see this example from oracle documentation
The following example calculates, for each manager in the sample table
hr.employees, a cumulative total of salaries of employees who answer to that
manager that are equal to or less than the current salary. You can see that Raphaely and Cambrault have the same cumulative total. This is because Raphaely and Cambrault have the identical salaries, so Oracle adds together their salary values and applies the same cumulative total to both rows.
SELECT manager_id, last_name, salary,
SUM(salary) OVER (PARTITION BY manager_id ORDER BY salary
RANGE UNBOUNDED PRECEDING) l_csum
FROM employees;
MANAGER_ID LAST_NAME SALARY L_CSUM
100 Mourgos 5800 5800
100 Vollman 6500 12300
100 Kaufling 7900 20200
100 Weiss 8000 28200
100 Fripp 8200 36400
100 Zlotkey 10500 46900
100 Raphaely 11000 68900
100 Cambrault 11000 68900
100 Errazuriz 12000 80900
149 Taylor 8600 30200
149 Hutton 8800 39000
149 Abel 11000 50000
201 Fay 6000 6000
205 Gietz 8300 8300
King 24000 24000
For clear understanding read the following point:
Whenever the order_by_clause results in identical
values for multiple rows, the function returns the same result for
each of those rows
ITS THE CUMULATIVE SUM HERE.
SO,IF TRY GIVING SAME NAME FOR ALL EMPLOYESS AND see the same result as you were getting with (partition by dept).
so , sum function which u are using here is analytic function and so results in cumulative sum. and when identical values are identified, same result is displayed.
Hope you got it!
Cheers,
Kishore KVR