Question

I’m sure someone will have a very simple answer to this but I can’t work it out for the life of me: I have 3 tables that look something like this:

Vehicles: Vehicle_id, Reg_number...
Datalogger: Logger_id, event, status, date...
Vehicle_Loggers: Vehicle_id, Logger_id, installed_from, installed_to

(Relationships are on columns with the same name here)

Using these tables how would I get the whole history of a given vehicle’s logs (event and status) even if it has had multiple loggers fitted at different times?

I know this can be done using a cursor but as this is really a set operation (Get the set of loggers that have been attached to the vehicle, then get the reports of each logger using the given date range for that logger)

EDIT: Loggers can be used in more than one vehicle during their lifetime, hence the inclusion of the dates.

Thanks

Gareth

Answer 1

You can do it like this:

select v.Reg_number, d.* from Vehicles v
inner join Vehicle_Loggers vl on vl.Vehicle_id = v.Vehicle_id
inner join Datalogger d on d.Logger_id = vl.Logger_Id
where v.Reg_number = ...

Just replace the Reg_number for the intended one.

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To take in account the dates, possibly would be like this:

select v.Reg_number, d.* from Vehicles v
inner join Vehicle_Loggers vl on vl.Vehicle_id = v.Vehicle_id
inner join Datalogger d on d.Logger_id = vl.Logger_Id and d.date between vl.installed_from and vl.installed_to
where v.Reg_number = ...