将数值赋给 varchar 后对一行的值求和

Question

我有两个 table，table_a 和 table_b，如下所示。

Table table_a:

  a_id |columna |varchar1|varchar2|varchar3
----------------------------------
|   1  |  a     | Medium |  High  | n/a 
|   2  |  b     | Low    |  n/a   | n/a
|   3  |  c     | Medium |  Low   | High

在table_a中每个varchar值被赋予一个数值：高为 1，中为 2，低为 3。

Table table_b:

  b_id |columna_fk|average
--------------------------
|   1  |  a       |
|   1  |  b       |
|   3  |  c       |

如何获取行的平均值（忽略 n/a）并更新 table_b 中的平均列？

例如见下面的table：

  b_id |columna_fk|average
--------------------------
|   1  |  a       | 1.5
|   1  |  b       | 3
|   3  |  c       | 2

Answer 1

一种方法是暴力破解：

update b
    set average = ((case varchar1 when 'High' then 1 when 'Medium' then 2 when 'Low' then 3 end) +
                   (case varchar2 when 'High' then 1 when 'Medium' then 2 when 'Low' then 3 end) +
                   (case varchar3 when 'High' then 1 when 'Medium' then 2 when 'Low' then 3 end)
                  ) /
                  nullif((case varchar1 when 'n/a' then 0 else 1 end) +
                         (case varchar2 when 'n/a' then 0 else 1 end) +
                         (case varchar3 when 'n/a' then 0 else 1 end)
                        )
    from a
    where a.columna = b.columna_fk;

Answer 2

感谢您的回答，我做了一些改动，它对我有用。下面是我的零钱。

update b
set average = 
(case when 
((case varchar1 when 'High' then 1 when 'Medium' then 2 when 'Low' then 3 else 0 end) +
 (case varchar2 when 'High' then 1 when 'Medium' then 2 when 'Low' then 3 else 0 end) +
 (case varchar3 when 'High' then 1 when 'Medium' then 2 when 'Low' then 3 else 0 end)) <> 0 
then
((case varchar1 when 'High' then 1 when 'Medium' then 2 when 'Low' then 3 else 0 end) +
 (case varchar2 when 'High' then 1 when 'Medium' then 2 when 'Low' then 3 else 0 end) +
 (case varchar3 when 'High' then 1 when 'Medium' then 2 when 'Low' then 3 else 0 end)) 
/
((case varchar1 when 'n/a' then 0 else 1 end) +
 (case varchar2 when 'n/a' then 0 else 1 end) +
 (case varchar3 when 'n/a' then 0 else 1 end))
else null end)
from a where a.columna = b.columna_fk;

将数值赋给 varchar 后对一行的值求和

Sum values of a row after giving a numeric value to a varchar

sql

postgresql

postgresql-9.2

postgresql-9.3