如何在不使用分组依据的情况下用平均值替换空值？

Question

假设有一个表demoa，其中包含以下数据：

date        a           b            c  
2017-05-22  1           6           10  
2017-05-23  2           7           11  
2017-05-24  3           8           12  
2017-05-25  4           9           null
2017-05-26  5           null        null
2017-05-27  null        null        null

我想null用其相应列的平均值替换这些值：

date        a           b            c
2017-05-22  1           6           10
2017-05-23  2           7           11
2017-05-24  3           8           12
2017-05-25  4           9           11
2017-05-26  5           7.5         11
2017-05-27  3           7.5         11

我尝试nvl使用avg()，但这需要group by每一列并且无法删除null值：

select 
    date,
    nvl(a,avg(a)),
    nvl(b,avg(b)),
    nvl(c,avg(c))
from damoa
group by date,a,b,c;

任何帮助表示赞赏。

Answer 1

Windows 功能 - avg(...) over ()

select  dt
       ,coalesce (a,avg(a) over ())  as a
       ,coalesce (b,avg(b) over ())  as b
       ,coalesce (c,avg(c) over ())  as c

from    demoa    

+------------+-----+-----+------+
|     dt     |  a  |  b  |  c   |
+------------+-----+-----+------+
| 2017-05-22 | 1.0 | 6.0 | 10.0 |
| 2017-05-23 | 2.0 | 7.0 | 11.0 |
| 2017-05-24 | 3.0 | 8.0 | 12.0 |
| 2017-05-25 | 4.0 | 9.0 | 11.0 |
| 2017-05-26 | 5.0 | 7.5 | 11.0 |
| 2017-05-27 | 3.0 | 7.5 | 11.0 |
+------------+-----+-----+------+