Analytic Functions :
Analytic functions compute an aggregate value based on a group of rows. They differ from aggregate functions in that they return multiple rows for each group. The group of rows is called a window and is defined by the analytic_clause. For each row, a sliding window of rows is defined. The window determines the range of rows used to perform the calculations for the current row. Window sizes can be based on either a physical number of rows or a logical interval such as time.
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.
Analytic functions are commonly used to compute cumulative, moving, centered, and reporting aggregates.
Example:
SELECT ename "Ename", deptno "Deptno", sal "Sal",
SUM(sal)
OVER (ORDER BY deptno, ename) "Running Total",
SUM(SAL)
OVER (PARTITION BY deptno
ORDER BY ename) "Dept Total",
ROW_NUMBER()
OVER (PARTITION BY deptno
ORDER BY ENAME) "Seq"
FROM emp
ORDER BY deptno, ename
SELECT * FROM (
SELECT deptno, ename, sal, ROW_NUMBER()
OVER (
PARTITION BY deptno ORDER BY sal DESC
) Top3 FROM emp
)
WHERE Top3 <= 3
SELECT * FROM (
SELECT deptno, ename, sal,
DENSE_RANK()
OVER (
PARTITION BY deptno ORDER BY sal desc
) TopN FROM emp
)
WHERE TopN <= 3
ORDER BY deptno, sal DESC
Aggregate Functions :
Aggregate functions return a single result row based on groups of rows, rather than on single rows. Aggregate functions can appear in select lists and in ORDER BY and HAVING clauses. They are commonly used with the GROUP BY clause in a SELECT statement, where Oracle Database divides the rows of a queried table or view into groups. In a query containing a GROUP BY clause, the elements of the select list can be aggregate functions, GROUP BY expressions, constants, or expressions involving one of these. Oracle applies the aggregate functions to each group of rows and returns a single result row for each group.
If you omit the GROUP BY clause, then Oracle applies aggregate functions in the select list to all the rows in the queried table or view. You use aggregate functions in the HAVING clause to eliminate groups from the output based on the results of the aggregate functions, rather than on the values of the individual rows of the queried table or view.
Example:
Aggregate functions are sum(), count(), avg(), max(), min() like:
select sum(sal) , count(*) , avg(sal) , max(sal) , min(sal) from emp;
