Sql 计算不同日期两个值之间的百分比差异

我已经创建了一个查询，其中包含最新更改的金额，但我还想包括新金额与前一个金额的比较是增加还是减少，以及前一个金额与当前金额之间的百分比。 这是我的疑问：

     SELECT 
        RATE.FK_ORGA_FRAN, 
        RATE.FK_ORGA_OPER,
        RATE.FED, 
        RATE.FK_RCOM, 
        RATE.FK_PROD,
        RATE.FK_CDIR,
        RATE.FK_TIER, 
        RATE.FK_TPRE, 
        RATE.FK_CURR, 
        RATE_STEP.UNIT_COST, 
        RATE.FK_CURR
    from RATE , RATE_STEP
    WHERE
        RATE.FK_ORGA_FRAN = RATE_STEP.FK_ORGA_FRAN AND
        RATE.FK_ORGA_OPER = RATE_STEP.FK_ORGA_OPER AND
        RATE.FK_RCOM = RATE_STEP.FK_RCOM AND
        RATE.FK_PROD = RATE_STEP.FK_PROD AND
        RATE.FK_CDIR = RATE_STEP.FK_CDIR AND
        RATE.FK_TIER = RATE_STEP.FK_TIER AND
        RATE.FK_TPRE = RATE_STEP.FK_TPRE AND
        RATE.FK_PMAT = RATE_STEP.FK_PMAT AND
        RATE.FED = RATE_STEP.FK_RATE_FED AND
        RATE.FED BETWEEN (SYSDATE) -16 AND (SYSDATE)

你能帮忙吗

非常感谢

---

Fred

假设您使用的是oracle SQL

样本数据如下：

DT              Rate
14-JAN-14        19
15-JAN-14        11
17-JAN-14        14
18-JAN-14        15
19-JAN-14        11
21-JAN-14        12
23-JAN-14        15

create table rate_log (dt date, rate number(5));

使用下面的查询并对其应用类似的逻辑

WITH data AS
  ( SELECT rownum rn, t.* FROM
    ( SELECT dt, rate FROM rate_log ORDER BY dt
    )t
  )
SELECT d1.dt,
  d1.rate,
  ROUND(( d1.rate - d2.rate ) * 100 / d1.rate, 2 )diff_perc,
  CASE
    WHEN(( d1.rate - d2.rate ) < 0 )
    THEN 'Increase'
    ELSE 'Decrease'
  END change
FROM data d1,
  data d2
WHERE( d1.rn - 1 ) =( d2.rn(+) )
ORDER BY d1.dt;

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如能对专栏进行更多解释，并提供您正在使用的dbms，将不胜感激。