getting latest data in one to many relation table - mysql

Question

i would like to fetch data from table a,b,c but order by most recent data of table response
table casework has this structure ( simplified):
casework_id | problem | user_id
------------+-----------+-------
1 | Problem1 | 1
2 | Problem2 | 2
3 | Problem3 | 1
4 | Problem4 | 3
table user has this structure ( simplified):
user_id | name
--------+-----------------
1 | peter
2 | Sam
3 | Tom
4 | Steve
table response has this structure ( simplified):
response_id | response | casework_id | created
------------+-----------+--------------+-------
1 | responce1 | 1 | 2012-10-14 11:28:31
2 | responce2 | 1 | 2012-9-10 11:28:31
3 | responce3 | 1 | 2012-9-2 11:28:31
4 | responce4 | 3 | 2012-8-3 11:28:31
4 | responce5 | 3 | 2012-8-2 11:28:31
I am looking the query to fetch data order by latest responce and group by casework_id
I. e. required out put is
casework_id | problem | name | responce | created
------------+-----------+-------+-----------+---------
1 | Problem1 | peter | responce1 | 2012-10-14 11:28:31
2 | Problem2 | Sam | Null | Null
3 | Problem3 | peter | responce4 | 2012-8-3 11:28:31
4 | Problem4 | Tom | Null | Null
I would be most grateful if one of you kind people could point me in the right direction.

Answer 1

You can use the following:
select c.casework_id,
c.problem,
u.name,
r2.response,
r1.created
from casework c
left join user u
on c.user_id = u.user_id
left join
(
select max(created) created, casework_id
from response r
group by casework_id
) r1
on c.casework_id = r1.casework_id
left join response r2
on r1.created = r2.created
and r1.casework_id = r2.casework_id
See SQL Fiddle with Demo
If you want to include both the user that created the casework and then who responsed, then you will want to join on the user table twice:
select c.casework_id,
c.problem,
u1.name CreatedByName,
r2.response,
r1.created,
u2.name ReponseName
from casework c
left join user u1
on c.user_id = u1.user_id
left join
(
select max(created) created, casework_id
from response r
group by casework_id
) r1
on c.casework_id = r1.casework_id
left join response r2
on r1.created = r2.created
and r1.casework_id = r2.casework_id
left join user u2
on r2.user_id = u2.user_id
See SQL Fiddle with demo

Answer 2

I have not tested it, but it might give you an idea
select c.casework_id, c.problem,
(select name from user u where u.user_id = c.user_id ),
(select r.reponse from response r where r.casework_id = c.casework_id ORDER BY r.created DESC LIMIT 1),
(select r.created from response r where r.casework_id = c.casework_id ORDER BY r.created DESC LIMIT 1),
from casework c

Answer 3

SELECT responce.casework_id, problem, name, responce, created
FROM responce
JOIN
(SELECT casework_id, problem, name
FROM casework JOIN user
ON casework.userid=user.userid) AS A
ON responce.casework_id=A.casework_id
ORDER BY responce, responce.casework_id

Answer 4

Try this
select c.caseword_id, c.problem, u.name, response.response, responce.created from asework c inner join user u on u.user_id = c.user_id left outer join select casework_id from response having max(created) group by casework_id) responsedata on responsedata.casework_id = c.casework_id