SQLite 将多个查询与共享列组合

Question

我正在尝试编写一个 SQLite 查询来获取一个值的总出现次数，除以月数。

所需输出的示例：

Name   Jun  Jul  Aug  Sept
John   3    2    5    2
Robert 4    12   45   22
Linda  0    2    1    0

我希望Name 字段只返回唯一的结果，所以它基本上每次在六月、七月等月份出现“约翰”时都会计算在内。

这是我到目前为止所拥有的，使用我的实际数据库。它可以返回正确的列和唯一的“ReasonDetail”，但计数不准确：

SELECT * FROM

(
    SELECT ReasonDetail AS Appetite, COUNT(*) AS June
        FROM CallRecords
        WHERE CallReason = 'Appetite Question'
        AND DateTime BETWEEN  '2017-06-01 00:00' AND '2017-07-01 00:00'
        GROUP BY ReasonDetail
),
(
    SELECT COUNT(*) AS July
        FROM CallRecords
        WHERE CallReason = 'Appetite Question'
        AND DateTime BETWEEN  '2017-07-01 00:00' AND '2017-08-01 00:00'
        GROUP BY ReasonDetail
),
(
    SELECT COUNT(*) AS August
        FROM CallRecords
        WHERE CallReason = 'Appetite Question'
        AND DateTime BETWEEN  '2017-08-01 00:00' AND '2017-09-01 00:00'
        GROUP BY ReasonDetail
)
GROUP BY Appetite

我在这里做错了什么？在这种情况下，有没有更好的方法来编译正确的计数？

谢谢！

Answer 1

这称为条件聚合。在聚合函数中使用case 表达式。

SELECT ReasonDetail AS Appetite
,COUNT(CASE WHEN DateTime>='2017-06-01 00:00' AND DateTime<'2017-07-01 00:00' THEN 1 END) AS June
,COUNT(CASE WHEN DateTime>='2017-07-01 00:00' AND DateTime<'2017-08-01 00:00' THEN 1 END) AS July
,COUNT(CASE WHEN DateTime>='2017-08-01 00:00' AND DateTime<'2017-09-01 00:00' THEN 1 END) AS August
FROM CallRecords
WHERE CallReason = 'Appetite Question'
GROUP BY ReasonDetail