Oracle窗口从句
对Oracle窗口一直搞不清楚，最近看了Laurent Schneider 写的"Advanced SQL Programming"一书对于这部分的描述，感觉写的很清楚，故摘译下来，以备查看。窗口
partition从句并不是限制分析函数运算范围的唯一方法。当使用ROWS BETWEEN从句时，行就会被排序，一个窗口就会被定义。
SELECT ENAME, HIREDATE, SAL, MAX ( SAL ) OVER ( ORDER BY HIREDATE, ENAME ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING ) MAX_BEFORE, MAX ( SAL ) OVER ( ORDER BY HIREDATE, ENAME ROWS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING ) MAX_AFTERFROM EMPORDER BY HIREDATE, ENAME;
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