Question

I have a mysql query. I need to get last value from columns Lat,Lng from my table but serial_number column needs to be distinct.

How to make such a query?

This is needed as I am using this coordinates to load it to Google map. So when the Google maps loads I need to have a marker on each last coordinates where vehicle is.

Answer 1

SELECT  m.*
FROM    (
        SELECT  DISTINCT serial_number
        FROM    mytable
        ) md
JOIN    mytable m
ON      m.id =
        (
        SELECT  id
        FROM    mytable mi
        WHERE   mi.serial_number = md.serial_number
        ORDER BY
                mi.time DESC, mi.id DESC
        LIMIT   1
        )

Create an index on (serial_number, time, id) for this to work fast.

If you want to retrieve the last record for a certain serial_number, just use this:

SELECT  *
FROM    mytable
WHERE   serial_number = :my_serial_number
ORDER BY
        time DESC, id DESC
LIMIT   1