psql - 查询 PSQL 确定系统当前时间的患者数量

Question

select room_id,count (distinct(patient_id)) as patient_id 
from patient_flow where time='CURRENT_TIME'; 

我需要当前时间具有相应 room_ids 的患者 ID 数。

 id | patient_id  | room_id |        time
----+-------------+---------+---------------------
  1 | 00035-67351 |       1 | 2015-06-09 10:11:20
  1 | 00035-67351 |       2 | 2015-06-09 10:31:20
  1 | 00035-67351 |       1 | 2015-06-09 10:12:20
  1 | 00035-67351 |       1 | 2015-06-09 10:12:40
  1 | 00035-67351 |       1 | 2015-06-09 10:15:40
  1 | 00035-67351 |       1 | 2015-06-09 10:30:40
  1 | 00035-67351 |       2 | 2015-06-09 10:32:40
  1 | 00035-67351 |       2 | 2015-06-09 10:36:40
  1 | 00035-67351 |       2 | 2015-06-09 10:38:40
  1 | 00035-67351 |       2 | 2015-06-09 10:50:40

我写了上面的查询，但它没有执行。

Answer 1

select current_time, room_id, count (distinct(patient_id)) as patient_id from patient_flow  group by room_id;

我在执行上述查询时得到了结果..

Answer 2

您错过了GROUP BY使用 with aggregate function 时的情况COUNT()。以下查询将起作用：

SELECT room_id, COUNT (DISTINCT(patient_id)) AS patient_id 
FROM patient_flow 
WHERE time = CURRENT_DATE
GROUP BY room_id;