如何在SQL视图中将计数和总和表示为列？

Question

基本上我在定义的PostgreSQL中有mytable

id integer,
ownername text,
length integer,
status integer

预期的结果是创建一个视图，每个所有者名称行将具有以下列

 ownername  | count_in_status1 | sum_length_status1 | count_in_status2 | sum_length_status2 | count_in_status3 | sum_length_status3 | ..... | total_count | total_sum_length 

有点难以解释，但基本上我需要每个所有者名称的计数和总和，最后需要总计数和总长度。 目前，实际上有5种状态

尝试以下

create view myview as     
select ownername, status, count(*), sum(length) from mytable group by ownername, status

这将返回数据，但不会以我上面介绍的最有效的方式返回。 如何实现呢？

Answer 1

我认为这是您想要的：

create view myview as     
    select ownername, 
           count(*) filter (where status = 1) as cnt_status_1,
           sum(length) filter (where status = 1) as len_status_1,
           count(*) filter (where status = 2) as cnt_status_2,
           sum(length) filter (where status = 2) as len_status_2,
           . . .  -- continue for each status
           count(*) as cnt,
           sum(length) as length
    from mytable
    group by ownername;

Answer 2

使用Filter是一个很好的解决方案（请参阅@Gordon Linoff响应）

与许多数据库更加兼容，yan也可以编写：

create view myview as     
select ownername,
       sum(case when status = 1 then 1      else 0 end) as cnt_status_1,
       sum(case when status = 1 then length else 0 end) as len_status_1,
       sum(case when status = 1 then 1      else 0 end) as cnt_status_2,
       sum(case when status = 1 then length else 0 end) as len_status_2,           
       . . .  -- continue for each status
       count(*) as cnt,
       sum(length) as length
from mytable
group by ownername;