PostgreSQL合并计数和分组结果

上述SQL查询提供以下输出：

select type, created_at::date , count(type)
from txns
group by created_at::date, type
order by created_at::date;

  type   | created_at | count 
---------+------------+-------
 full    | 2017-05-20 |     2
 virtual | 2017-05-20 |     2
 full    | 2017-05-21 |     1
 virtual | 2017-05-21 |     1
 full    | 2017-05-22 |     3

如何通过

created\u at

对上述结果进行分组，以获得以下输出：

select type, created_at::date , count(type)
from txns
group by created_at::date, type
order by created_at::date;

  type   | created_at | count 
---------+------------+-------
 full    | 2017-05-20 |     2
 virtual | 2017-05-20 |     2
 full    | 2017-05-21 |     1
 virtual | 2017-05-21 |     1
 full    | 2017-05-22 |     3

我想通过在创建的

在一行中获取
完整
和
虚拟
类型计数。
这应该可以：

 created_at | full_count | virtual_count
------------+-----------------
 2017-05-20 |     2     |  2
 2017-05-21 |     1     |  1
 2017-05-22 |     3     |  0

如果您有两种以上的类型，并且在进一步处理过程中，您可以处理hstore：

with so as (
select type, created_at::date , count(type) from txns group by created_at::date, type order by created_at::date
)
 select
  created_at
, sum(case when type = 'full' then count else 0 end) full_count
, sum(case when type = 'virtual' then count else 0 end) virtual_count
from so
group by created_at;

 created_at | full_count | virtual_count
------------+------------+---------------
 2017-05-20 |          2 |             2
 2017-05-21 |          1 |             1
 2017-05-22 |          3 |             0
(3 rows)

我将在不使用CTE/子查询的情况下执行此操作，如下所示：

WITH q AS ( SELECT type, created_at::date , count(type) FROM txns GROUP BY 1,2)
SELECT created_at, hstore(array_agg(type), array_agg(count::text))
FROM q GROUP BY 1;

Postgres通常实现CTE，因此这甚至可能有轻微的性能优势

注意：您也可以在较新版本的Postgres中使用
过滤器
：

select created_at::date,
       sum( (type = 'Full')::int ) as cnt_full,
       sum( (type = 'Virtual')::int ) as cnt_virtual
from txns
group by created_at::date
order by created_at::date;

你太棒了，谢谢！等待其他结果其他方面我会接受它非常感谢。这个解决方案更好，而且“类型”不应该在组中。