How to Select the Most Recent Sensor Data Based on Timestamps?

Selecting Recent Values Based on Timestamp Keys

Your initial approach using GROUP BY and max() was correct in principle, but the SQL syntax requires including non-aggregated columns in the GROUP BY clause or using them in an aggregate function.

The correct solution includes selecting the maximum timestamp for each sensor and then using that in a subquery to retrieve the corresponding sensor data:

SELECT sensorID,
       MAX(timestamp) AS latest_timestamp,
       sensorField1,
       sensorField2
FROM sensorTable
GROUP BY sensorID

This query retrieves the maximum timestamp for each sensor. You can then use this subquery in a nested query to retrieve all sensors with that timestamp:

SELECT *
FROM sensorTable
WHERE timestamp = (
    SELECT MAX(timestamp)
    FROM sensorTable
    WHERE sensorID = sensorTable.sensorID
)

This second query results in a single row for each sensor, with the most recent timestamp and associated sensor data.

The above is the detailed content of How to Select the Most Recent Sensor Data Based on Timestamps?. For more information, please follow other related articles on the PHP Chinese website!