Analytical Functions:FIRST and LAST

The FIRST and LAST functions can be used to return the first or last value from an ordered sequence. Say we want to display the salary of each employee, along with the lowest and highest within their department we may use something like.

SELECT
EMPNO,
DEPTNO,
SAL
       MIN(sal) KEEP (DENSE_RANK FIRST ORDER BY sal) OVER (PARTITION BY deptno) SAL_LOW
       MAX(sal) KEEP (DENSE_RANK LAST ORDER BY sal) OVER (PARTITION BY deptno) SAL_HIGH
FROM   emp
ORDER BY deptno, sal;