"keep" feature

Question

what's the meaning of this feature?
when i see something like this
SELECT last_name, department_id, salary,
       MIN(salary) KEEP (DENSE_RANK FIRST ORDER BY commission_pct)
          OVER (PARTITION BY department_id) "Worst",
       MAX(salary) KEEP (DENSE_RANK LAST ORDER BY commission_pct)
          OVER (PARTITION BY department_id) "Best"
FROM employees
ORDER BY department_id, salary;i think it could be done also like this:
SELECT last_name, department_id, salary,
       MIN(salary)           OVER (PARTITION BY department_id ORDER BY commission_pct) "Worst",
       MAX(salary)           OVER (PARTITION BY department_id ORDER BY commission_pct) "Best"
FROM employees
ORDER BY department_id, salary;what's the difference?

Answer 1

These two queries give me different results.
DB version Connected to Oracle Database 10g Enterprise Edition Release 10.2.0.3.0
Column names modified to adapt to EMP table of scott.
SELECT ename, deptno, sal,
       MIN(sal) KEEP (DENSE_RANK FIRST ORDER BY comm)
          OVER (PARTITION BY deptno) "Worst",
       MAX(sal) KEEP (DENSE_RANK LAST ORDER BY comm)
          OVER (PARTITION BY deptno) "Best"
FROM emp
ORDER BY deptno, sal;
SELECT ename, deptno, sal,comm,
       MIN(sal)           OVER (PARTITION BY deptno ORDER BY comm) "Worst",
       MAX(sal)           OVER (PARTITION BY deptno ORDER BY comm) "Best"
FROM emp
ORDER BY deptno, sal;YOu may want to check again.
Keep is normally be used with first and last value (By Me :) )
Here is the link
[http://download-uk.oracle.com/docs/cd/B19306_01/server.102/b14200/functions001.htm]
run these two queries in scott and you will know the difference
SELECT ename, deptno, sal,
       MIN(sal) KEEP (DENSE_RANK FIRST ORDER BY comm NULLS LAST)
          OVER (PARTITION BY deptno) "Worst",
       MAX(sal) KEEP (DENSE_RANK LAST ORDER BY comm NULLS LAST)
          OVER (PARTITION BY deptno) "Best"
FROM emp
ORDER BY deptno, sal;
SELECT ename, deptno, sal,comm,
       MIN(sal)   OVER (PARTITION BY deptno ORDER BY comm NULLS LAST) "Worst",
       MAX(sal)           OVER (PARTITION BY deptno ORDER BY comm NULLS LAST) "Best"
FROM emp
ORDER BY deptno, sal;You will see in teh query where KEEP is used it will keep the first row it finds for all the rows of that departments
the query where KEEPis not used it treats two rows in dept 30 differently since they have commission NULL and assinga a different BEST and WORST for them
than rest of the emp's in the same department.
Cheers!!!
Bhushan
Edited by: Buga on Feb 4, 2010 5:02 PM: added LInk
Edited by: Buga on Feb 4, 2010 5:12 PM.. Explanation in second part added