MySQL LEFT JOIN dates with order - mysql

Question

I have a following tables:
sensors:
id name key code
1 s1 abc 123
2 s2 def 456
3 s3 ghi 789
measurements:
id value sensor_id generated_at
1 1.0 1 2013-12-30 06:00:00
2 1.0 1 2013-12-30 06:01:00
3 1.0 1 2013-12-30 06:02:00
4 3.0 2 2013-12-30 07:00:00
5 3.0 2 2013-12-30 07:01:00
6 3.0 2 2013-12-30 07:05:00
7 5.0 3 2013-12-30 08:02:00
8 5.0 3 2013-12-30 08:03:00
9 5.0 3 2013-12-30 08:11:00
10 5.0 3 2013-12-30 08:15:00
What I want to do is to generate report with all sensors data and include first and last generated_at time for received measurements, so the result of MySQL request should look like:
id name key code first_value_generated_at last_value_generated_at
1 s1 abc 123 2013-12-30 06:00:00 2013-12-30 06:02:00
2 s2 def 456 2013-12-30 07:00:00 2013-12-30 07:05:00
3 s3 ghi 789 2013-12-30 08:02:00 2013-12-30 08:15:00
I would appreciate any help, thanks.

Answer 1

I don't think that LEFT JOIN is really necessary here (only in case when there more or less sensors.id than in measurements.sensor_id). SQL query is below :
SELECT
s.id,
s.name,
s.key,
s.code,
m.first_value_generated_at,
m.last_value_generated_at
FROM sensors s JOIN
(SELECT
sensor_id,
MIN(generated_at) as first_value_generated_at,
MAX(generated_at) as last_value_generated_at
FROM
measurements
GROUP BY
sensor_id
) m ON s.id = m.sensor_id
ORDER BY
s.id

Answer 2

I hope this should work for you,
select *
,(select min(generated_at) from measurements as a where a.sensor_id =s.id) as first_value_generated_at
,(select max(generated_at) from measurements as b where b.sensor_id =s.id) as last_value_generated_at
from sensors as s

Answer 3

Try this query , it will generate the exact output you need
select s.id,s.name,s.key,s.code,min(m.generated_at) first_vaue_generated_at,max(m.generated_at) last_value_generated_at
from sensors s
LEFT JOIN measurements m ON (s.id = m.sensor_id)
group by 1,2,3,4;

Answer 4

Try this it will work
select s.id,s.name,s.key,s.code,m.generated_at as first_value_generated_at,ml.generated_at as last_value_generated_at from sensors as s,measurements as mf,measurements as ml where s.id = mf.sessor_id and s.id = ml.sensor_id and mf.generated_at < ml.generated_at group by mf.sensor_id

Answer 5

Maybe this could do that - nested selects?
select sensors.id, sensors.name, sensors.key, sensors.code,
( select generated_at from measurements order by time asc limit 1 )
as first_value_generated_at,
( select generated_at from measurements order by time desc limit 1 )
as last_value_generated_at from sensors