Nick Sinas Nick Sinas - 3 months ago 6
SQL Question

Simple Query to Grab Max Value for each ID

OK I have a table like this:

ID Signal Station OwnerID
111 -120 Home 1
111 -130 Car 1
111 -135 Work 2
222 -98 Home 2
222 -95 Work 1
222 -103 Work 2


This is all for the same day. I just need the Query to return the max signal for each ID:

ID Signal Station OwnerID
111 -120 Home 1
222 -95 Work 1


I tried using MAX() and the aggregation messes up with the Station and OwnerID being different for each record. Do I need to do a JOIN?

Answer

Something like this? Join your table with itself, and exclude the rows for which a higher signal was found.

select cur.id, cur.signal, cur.station, cur.ownerid
from yourtable cur
where not exists (
    select * 
    from yourtable high 
    where high.id = cur.id 
    and high.signal > cur.signal
)

This would list one row for each highest signal, so there might be multiple rows per id.

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