如何在SQL中从同一列中划分两个值

Question

正如标题所述,我想将两个值彼此分开,这两个值在同一列中.例如

    A             B              C            D
  Shirts         2011           85            0
  Shirts         2012           92      percent change from 2011 to 2012
  Shirts         2013          100      percent change from 2012 to 2013
  Pants          2011           31            0
  Pants          2012           42      percent change from 2011 to 2012
  Pants          2013           55      percent change from 2012 to 2013
  Jacket         2011           10            0
  Jacket         2012           16      percent change from 2011 to 2012
  Jacket         2013           18      percent change from 2012 to 2013

在此示例中,列D将从C列派生,其中2012的值从2011中减去,然后乘以100得到百分比.

我不知道如何设置查询我尝试做了一堆子查询,但不知道如何将它们链接在一起.任何帮助将不胜感激.

Answer 1

这是一个获得您想要的东西的选项

SELECT t1.a, t1.b, t1.c,
    CASE WHEN t2.c IS NULL THEN 0 ELSE t1.c - t2.c END AS d,
    CASE WHEN t2.c IS NULL THEN 0 ELSE (1.0 * t1.c - t2.c) / t1.c * 100.0 END AS pct
FROM t t1
LEFT OUTER JOIN t t2 ON t1.a = t2.a
    AND t1.b = t2.b + 1

SQL 小提琴示例