case语句返回null postgresql时处理空值

Question

我有一个名为check_n的表，我有城市和价值

我写了一个查询，里面有CASE语句。以下是我的查询

select city,
       CASE when (value/10)::integer = 2 
       then 2 END as a,
       CASE when (value/10)::integer = 5 
       then 5 END as b,
       CASE when (value/10)::integer = 3 
       then 3 END as c
from check_n;

在下面的image中附加输出

我想要输出如下：

city, a, b, c
glb, 2, 5, 3

任何帮助表示赞赏。我正在使用Postgresql 9.5

另外如果我有另一个表chck_n如何使用该函数：

 city |  fact  | value 
------+--------+-------
glb  | male   | 22000
glb  | female | 23000
glb  | total  | 45000

我想使用这个查询：

SELECT city,
      CASE WHEN fact = 'male'
           THEN value
      END as males,
      CASE WHEN fact= 'female'
           THEN value
      END as females,
      CASE WHEN fact ='total'
           THEN value
      END as total
FROM chck_n;

Answer 1

如果你想要每个城市一个结果，你可以这样做：

SELECT city,
       CASE WHEN 2 =ANY (array_agg((value/10)::integer))
            THEN 2
       END as a,
       CASE WHEN 5 =ANY (array_agg((value/10)::integer))
            THEN 5
       END as b,
       CASE WHEN 3 =ANY (array_agg((value/10)::integer))
            THEN 3
       END as c
FROM check_n
GROUP BY city;

 city | a | b | c 
------+---+---+---
 glb  | 2 | 5 | 3
(1 row)

Answer 2

我假设你的数据集：

with ds as (
select city,
       CASE when (value/10)::integer = 2 
       then 2 END as a,
       CASE when (value/10)::integer = 5 
       then 5 END as b,
       CASE when (value/10)::integer = 3 
       then 3 END as c
from check_n)
select distinct city, max(a)a, max(b) b, max(c) c
from ds
group by city