GROUP BY外键和日期范围

Question

我正在使用称为appointments的表，这些表是：

cheduled_at：datetime doctor_id：整数描述：文本finished_at：datetime

我想获得按doctor_id分组的所有约会的doctor_id ，以及根据一组日期间隔分组的所有约会的doctor_id ，这些时间间隔根据给定的输入集而变化。 我得到的输入是： from它是一个日期， to这也是一个日期。

第一次使用情况下，我想解决由月从给定的拆分结果from和to 。 因此，如果我from ='2018-02-03' to ='2018-10-03'，我想获取每个医生以及从2018-02到2018-02每个月完成的所有约会的计数2018-10 。

我知道如何按Doctor_id进行分组，但是我不知道如何对这些动态日期间隔进行分组。

这是我到目前为止的内容：

SELECT COUNT(*) FROM appointments WHERE finished_at IS NOT NULL GROUP BY doctor_id

我知道，如果事先有间隔，我可以执行尽可能多的查询，因此最终我每个月都要进行一次查询，例如：

SELECT COUNT(*) FROM appointments WHERE finished_at IS NOT NULL AND scheduled_at BETWEEN '2018-02-01' AND '2018-03-01' GROUP BY doctor_id

SELECT COUNT(*) FROM appointments WHERE finished_at IS NOT NULL AND scheduled_at BETWEEN '2018-03-01' AND '2018-04-01' GROUP BY doctor_id

我只是想知道是否有一种方法可以在SQL中做到这一点，所以我只需要执行一个查询。

Answer 1

您可以使用条件聚合：

SELECT doctor_id,
       SUM(CASE WHEN scheduled_at BETWEEN '2018-02-01' AND '2018-03-01' THEN 1 ELSE 0 END),
       SUM(CASE WHEN scheduled_at BETWEEN '2018-03-01' AND '2018-04-01' THEN 1 ELSE 0 END)    
FROM appointments
WHERE finished_at IS NOT NULL
GROUP BY doctor_id

Answer 2

用case表达式进行条件聚合 ：

SELECT doctor_id,
       COUNT(*),
       COUNT(case when scheduled_at BETWEEN '2018-02-01' AND '2018-03-01' then 1 end),
       COUNT(case when scheduled_at BETWEEN '2018-03-01' AND '2018-04-01' then 1 end)
FROM appointments
WHERE finished_at IS NOT NULL
GROUP BY doctor_id

或者也有group by年和月group by的查询：

SELECT doctor_id, year(scheduled_at), month(scheduled_at), COUNT(*)
FROM appointments
WHERE finished_at IS NOT NULL
GROUP BY doctor_id, year(scheduled_at), month(scheduled_at)

或者，也许应该使用ANSI SQL函数EXTRACT ：

SELECT doctor_id,
       extract(year from scheduled_at), extract(month from scheduled_at), COUNT(*)
FROM appointments
WHERE finished_at IS NOT NULL
GROUP BY doctor_id, extract(year from scheduled_at), extract(month from scheduled_at)

Answer 3

如果您的postgres版本是9.4或更高版本，则应考虑使用FILTER谓词，它比case语句更易于阅读且性能更高。

SELECT doctor_id,
       COUNT(*) AS total,
       COUNT(*) FILTER (WHERE scheduled_at BETWEEN '2018-02-01' AND '2018-03-01') AS date_feb,
       COUNT(*) FILTER (WHERE scheduled_at BETWEEN '2018-03-01' AND '2018-04-01') AS date_mar
FROM appointments
WHERE finished_at IS NOT NULL
GROUP BY doctor_id