确定当前记录和下一条记录之间相差的天数

创建测试用表：

CREATE OR REPLACE VIEW v AS
SELECT '1' AS id, DATE'2015-1-1' AS hiredate FROM DUAL
UNION ALL
SELECT '2' AS id, DATE'2015-5-1' AS hiredate FROM DUAL
UNION ALL
SELECT '3' AS id, DATE'2015-3-1' AS hiredate FROM DUAL;

SELECT * FROM v;

首先需要把下一条记录的雇佣日期移到当前行，这里需要用到 lead() over() 分析函数：

SELECT id, hiredate, LEAD(hiredate) OVER(ORDER BY hiredate) next_hd FROM v;

当数据提取到同一行后，在计算就比较简单了：

SELECT id, hiredate, next_hd - hiredate AS diff
  FROM (SELECT id, hiredate, LEAD(hiredate) OVER(ORDER BY hiredate) next_hd
          FROM v);

和lead对应的就是lag函数，如果能记住两个函数的区别当然比较好，如果记不住，可直接实验。

SELECT id,
       hiredate,
       LEAD(hiredate) OVER(ORDER BY hiredate) lead_hd,
       hiredate,
       LAG(hiredate) OVER(ORDER BY hiredate) lag_hd
  FROM v;