在列之间切换数据答案

【问题标题】：Switch data between columns在列之间切换数据
【发布时间】：2012-09-10 21:21:20
【问题描述】：

以下面的示例代码为例：

with test as (
    select to_date('01/2012', 'mm/yyyy') as dt, '1' as value from dual union all 
    select to_date('02/2012', 'mm/yyyy') as dt, '10' as value from dual union all 
    select to_date('03/2012', 'mm/yyyy') as dt, '100' as value from dual union all 
    select to_date('04/2012', 'mm/yyyy') as dt, '2' as value from dual union all 
    select to_date('05/2012', 'mm/yyyy') as dt, '20' as value from dual 
)
select dt, value from test

DT          | VALUE
1/1/2012    | 1
2/1/2012    | 10
3/1/2012    | 100
4/1/2012    | 2
5/1/2012    | 20

我希望我可以建立一个包含每条记录的先前值的新列，例如：

DT          | VALUE  | Previous
1/1/2012    | 1      | -
2/1/2012    | 10     | 1
3/1/2012    | 100    | 10
4/1/2012    | 2      | 100
5/1/2012    | 20     | 2

这似乎很简单，尽管我经常迷失在 connect_by 语句中。

有人可以帮忙吗？

【问题讨论】：

标签： sql date oracle11g connect-by

【解决方案1】：

无需使用CONNECT BY。你只需要一个LAG

SQL> ed
Wrote file afiedt.buf

  1  with test as (
  2      select to_date('01/2012', 'mm/yyyy') as dt, '1' as value from dual union all
  3      select to_date('02/2012', 'mm/yyyy') as dt, '10' as value from dual union all
  4      select to_date('03/2012', 'mm/yyyy') as dt, '100' as value from dual union all
  5      select to_date('04/2012', 'mm/yyyy') as dt, '2' as value from dual union all
  6      select to_date('05/2012', 'mm/yyyy') as dt, '20' as value from dual
  7  )
  8  select dt,
  9         value,
 10         lag(value) over (order by dt) prior_value
 11*   from test
SQL> /

DT        VAL PRI
--------- --- ---
01-JAN-12 1
01-FEB-12 10  1
01-MAR-12 100 10
01-APR-12 2   100
01-MAY-12 20  2

【讨论】：