Question

EDIT. I missed the one main issue I was having. I want to display all the unique ‘device_MAC’ rows. So I want this query to output 3 rows (as per the original query). The issue I am having is connecting the data table to the remote_node table via dt_short = rn_short where the maximum timestamp for dt_short in the data table.

I am having trouble running a query on 3 tables (2 have many to many relations).

What I am trying to do:

1. Get each distinct rn_IEEE from the remotenodes table with the maximum timestamp (in the example this will get 3 rows with 3 distinct short addresses rn_short)
2. Join with the devicenames table on device_IEEE
3. Get each distinct dt_short from the data table with the maximum timestamp
4. Join dt_short with rn_short from the query above

Now the problem I am running into is that I can do the queries for the above individually, I have even gotten the first 3 of them together into a query but I cannot seem to properly join the last bit of data to get the result that I want.

I have been going in circles trying to solve this. Here is a link to SQL Fiddle which contains all the test data and the query as far as I got it, it does what i want for the first line but from table ‘data’ after the first line is NULL:

See this SQL fiddle

Answer 1

Thanks for all your answers everyone. I managed to solve the problem by using views.
It’s not the most efficient way but I think it will do for now.
Here is the SQL Fiddle link:

http://sqlfiddle.com/#!2/4076e/8