Selecting from two tables using inner joins with constraints

Question

I have two tables Service and Status. The service table only saves a name and an id

| id |  name |
|----|-------|
|  1 | Test1 |
|  2 | Test2 |

There is also a state table like this

| id | status | service_id |                 timestamp |
|----|--------|------------|---------------------------|
|  1 |     OK |          1 | October, 15 2015 09:03:07 |
|  2 |     OK |          1 | October, 15 2015 09:08:07 |
|  3 |     OK |          2 | October, 15 2015 10:05:23 |
|  4 |     OK |          2 | October, 15 2015 10:15:23 |

I want to get such data

| id |  name | status |                 timestamp |
|----|-------|--------|---------------------------|
|  1 | Test1 |     OK | October, 15 2015 09:08:07 |
|  2 | Test2 |     OK | October, 15 2015 10:15:23 |

Latest status with service data. I have tried this argument

SELECT ser.id, ser.name, a.status, a.timestamp
from Service ser
  inner join (select * from status
              order by Status.timestamp
              DESC limit 1) as a
    on a.service_id = ser.id

but I only get

| id |  name | status |                 timestamp |
|----|-------|--------|---------------------------|
|  2 | Test2 |     OK | October, 15 2015 10:15:23 |

How to change the statement to get what I want?

Answer 1

For each service, only used if no subsequent service exists NOT EXISTS Return status:

select ser.id, ser.name, st.status, st.timestamp
from service ser
  left join status st1 on ser.id = st1.service_id
where not exists (select 1 from status st2
                  where st2.service_id = st1.service_id
                    and st2.timestamp > st1.timestamp)

You can choose to execute LEFT JOIN to return a service without any status. If not required, switch to JOIN.

Answer 2

You can do this:

SELECT 
  ser.id, 
  ser.name, 
  s.status, 
  s.timestamp 
FROM Service ser 
INNER JOIN status as s ON s.service_id = ser.id
INNER JOIN
(
   SELECT
     service_id, 
     MAX(timestamp) AS MaxDate
   FROM status 
   GROUP BY service_id
) AS a  ON a.service_id = s.service_id 
       AND a.MaxDate = s.timestamp;

Join with subquery:

SELECT
  service_id, 
  MAX(timestamp) AS MaxDate
FROM status 
GROUP BY service_id

Will eliminate all statuses except the latest date.