Question

我有一个包含表格的医院数据库：

equipment

id CHAR(40) NOT NULL, model CHAR(20) NOT NULL, serialno VARCHAR(20) NOT NULL, release_date DATE, PRIMARY KEY (id)

和

appointmentrelations
appointment_id CHAR(40) NOT NULL, 
 medicine_id    CHAR(40) NOT NULL, 
 equipment_id   CHAR(40) NOT NULL,
 PRIMARY KEY (appointment_id, medicine_id, equipment_id), 
 FOREIGN KEY (appointment_id) REFERENCES appointment(id), 
 FOREIGN KEY (medicine_id)REFERENCES medicineprice(medicine_id), 
 FOREIGN KEY (equipment_id) REFERENCES equipment(id)

和其他一些表格。

表约定描述了医院的预约，并将设备与其中使用的药物相关联。

我想写一个查询，找出与他的年龄相关的最多使用的设备。

appointmentrelations
a1    m1    e1  
a2    m2    e2
a3    m3    e3
a4    m3    e3
a5    m4    e2

equipment
e1  model1  se1 2004-07-14
e2  model2  se2 2017-10-19
e3  model3  se3 2015-01-08

在上面的样本中，与他的年龄相关的使用最多的设备是e2。

我尝试了以下内容：

SELECT equipment_id, COUNT(DISTINCT appointment_id) AS ab
FROM appointmentrelations
GROUP BY equipment_id
ORDER BY ab DESC
LIMIT 1

计算每台设备的使用次数，但我不知道如何将其与设备年龄联系起来。

Answer 1

If i understand correctly, you can wrap your current query in subquery:

SELECT * 
FROM equipment e
WHERE id  = (SELECT equipment_id
             FROM appointmentrelations
             GROUP BY equipment_id
             ORDER BY COUNT(DISTINCT appointment_id) DESC
             LIMIT 1);

Answer 2

您可以使用内部联接来按使用情况获取所有结果顺序

  select e.id, count(DISTINCT a.appointment_id), e.model, e.date 
  from equipment e 
  inner join appointmentrelations a on a.appointment_id = e.id
  group by e.id , e.model, e.date 
  order by count(DISTINCT a.appointment_id) DESC

SQL Query用于查找与表中其他元素相关的最常见元素

2 个答案: