UNION ALL / UNION on Presto

Question

我正在使用宝藏数据进行数据分析，在presto db中使用联合语句遇到了问题。

我怎么才能一夜之间联合起来呢。我不理解文档。每次我尝试像这样做联合：

SELECT 
  COUNT(*) AS ReservationsCreated,
  resource
FROM
  reservation
WHERE
  type = 'create'
UNION
SELECT 
  COUNT(*) AS ReservationsDeleted,
  resource
FROM
  reservation
WHERE
  type = 'delete'
GROUP BY
  resource
;

我得到的输出格式如下：

SELECT 
  COUNT(*) AS ReservationsCreated,
  resource
FROM
  reservation
WHERE
  type = 'create'
UNION
SELECT 
COUNT(*) AS ReservationsDeleted,
resource
FROM
reservation
WHERE
type = 'delete'
GROUP BY
resource
;

错误是这样的：

'"resource"' must be an aggregate expression or appear in GROUP BY clause

我想我不理解Presto的语法。关于Union的文档非常令人困惑。感谢您的帮助。

Answer 1

正如错误所述，查询的第一部分缺少group by。

 SELECT COUNT(*) AS ReservationsCreated, resource
 FROM reservation
 WHERE type = 'create'
 group by resource
 UNION ALL
 SELECT COUNT(*) AS ReservationsDeleted, resource
 FROM reservation
 WHERE type = 'delete'
 GROUP BY resource

实际上，查询可以简化为使用条件聚合。

select 
 resource
,sum(case when type = 'create' then 1 else 0 end) as reservationscreated
,sum(case when type = 'delete' then 1 else 0 end) as reservationsdeleted
from reservation
group by resource