COUNT({ * | [ DISTINCT | ALL ] expr }) [ OVER (analytic_clause) ]
SELECT ENAME,
E.HIREDATE,
COUNT(EMPNO) OVER(ORDER BY HIREDATE RANGE BETWEEN 30 PRECEDING AND 30 FOLLOWING) AS CNT
FROM EMP E
WHERE TO_CHAR(HIREDATE,‘YYYY‘)=‘1981‘;
ENAME HIREDATE CNT
---------- ----------- ----------
ALLEN 1981/2/20 2
WARD 1981/2/22 2
JONES 1981/4/2 2
BLAKE 1981/5/1 2
CLARK 1981/6/9 1
TURNER 1981/9/8 2
MARTIN 1981/9/28 2
KING 1981/11/17 3
FORD 1981/12/3 3
JAMES 1981/12/3 3原文：http://www.cnblogs.com/wwxbi/p/4176624.html