mysql从2个表中计算最新记录答案

【问题标题】：mysql count latest record from 2 tablesmysql从2个表中计算最新记录
【发布时间】：2022-01-29 15:25:42
【问题描述】：

我有两张桌子

patient

id	name	room
1	Adam	A
2	Ben	B
3	Charles	A
4	David	C
5	Eugen	B

和表check：

id	id_patient	check_date	condition
1	1	2021-11-11	bad
2	2	2021-11-12	good
3	1	2021-11-17	good
4	3	2021-11-17	poor
5	4	2021-11-18	bad
6	5	2021-11-18	bad
7	3	2021-12-20	poor
8	4	2021-12-20	bad
9	5	2021-12-21	bad
7	1	2021-12-22	bad
8	2	2021-12-22	poor
9	3	2021-12-23	good

如何从最新的病情检查日期记录中按房间计数病人..需要这样的结果：

room	bad	good	poor
A	1	1	0
B	1	0	1
C	1	0	0

【问题讨论】：

试着解释你想要的结果，很难理解你想说什么！
需要从最新的检查结果记录中按房间计数。我需要第三张桌子这样的结果
哪个版本的 MySQL？

标签： mysql

【解决方案1】：

这应该可以工作

select room, 
       sum(case when result = "bad" then 1 else 0 end) as bad,
       sum(case when result = "good" then 1 else 0 end) as good,
       sum(case when result = "poor" then 1 else 0 end) as poor
from 
    (select c3.id, patient, room, checkdate, result 
     from checks c3
     inner join patients pt on pt.id = c3.patient
     where c3.id in
         (select id
          from checks c1
          where patient = c3.patient and 
                          (select max(checkdate) 
                           from checks c2  
                           where c2.patient = c1.patient) = checkdate)) ch

group by room

https://www.db-fiddle.com/f/irBJY8JwxPygQZj7LYPofv/4

【讨论】：