对给定记录使重复值为null

Question

我有一个表格yrstphn，其记录如下：

|  yr  | st | phn  |  
| 2012 | NV | 1234 |
| 2012 | NV | 2361 |
| 2012 | MD | 1234 |
| 2012 | MD | 2361 |
| 2012 | MA | 1234 |
| 2012 | MA | 2361 |

我想通过使用程序（sql或cursor）获得以下内容：

|  yr  | st | phn  |
| 2012 | NV | 1234 |
| null | MD | 2361 |
| null | MA | null |

欢迎任何建议。

Answer 1

您似乎希望将每列视为单独的列表。这不是真正的关系，但您可以在SQL中执行：

select max(yr) as yr, max(st) as st, max(phn) as phn
from ((select row_number() over (order by yr) as seqnum, yr, null as st, null as phn
       from t
       group by year
      ) union all
      (select row_number() over (order by yr) as seqnum, NULL, st, NULL
       from t
       group by year
      ) union all
      (select row_number() over (order by yr) as seqnum, NULL, NULL, phn
       from t
       group by year
      )
     ) t
group by seqnum
order by seqnum;