How to Retrieve the Latest Status for All Services Using an Inner Join?

Selecting from Two Tables with Inner Join for Latest Status

When you have two tables containing related data, it becomes necessary to retrieve specific information from both tables. In this scenario, you have two tables: Service and Status. The Service table stores names and IDs, while the Status table tracks the status and timestamps associated with each service.

To retrieve the latest status for each service, you can utilize an inner join operation. The goal is to combine rows from both tables based on the service_id column, ensuring that only the latest status information is returned.

Unfortunately, the query you mentioned only retrieves the latest status for the service with service_id = 2. To address this limitation and retrieve the latest status for all services, consider the following modified SQL statement:

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;

The subquery within the final inner join eliminates all but the statuses with the latest timestamps for each service. By comparing the service_ids and matching the latest timestamps, you can guarantee that the query returns the desired results:

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

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