如何在SQL视图中将计数组和总和表示为列？

基本上，我在Postgresql中定义了mytable

id integer,
ownername text,
length integer,
status integer

预期的结果是为每个ownername行创建一个具有以下列的视图

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

这有点难以解释，但基本上我需要一个计数和每个拥有者的总和，最后是一个总计数和长度的总和。目前实际上有5种状态

试过下面的

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

---

这将返回数据，但不是以我上面介绍的最有效的方式返回。如何实现它？

我想这就是你想要的：

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;

---

使用

过滤器

是一个优雅的解决方案（请参见@Gordon Linoff响应）

Te与许多数据库更兼容，yan还可以写：

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;

---

您不需要状态栏。@没有名字的马。谢谢。事实上，

filter（）

是标准的ISO SQL