Question

I have a MySQL database with a structure like this…

Site has many Sensors
Sensors has many SensorReadings

I want to get all Sensors for a Site and the last 5 SensorReadings for all those Sensors. I suspect I’m going to have to do something with a stored procedure and temporary tables (if they even exist in MySQL.

Answer 1

Possibly Something like…

SELECT reading,
       date
FROM   (select sensor_id,
               reading,
               date,
               @num := if(@sensor_id = sensor_id, @num + 1, 1) as row_number,
               @sensor_id := sensor_id                         as dummy
        from   sensor_readings
        order  by sensor_id,
                  date desc) T
WHERE  row_number<=5  

Please give your actual table structure(s) in your question.