AWS Athena SQL to group and find minimum in distinct rows - sql

Question

I have a query against AWS Athena and the core of it works great. My companies code is AA (field ACD) and our competitors codes are BB, CC and DD (field OCD). So for each distinct trip my company makes I get a series of similar trips from competitors. I end up with a table like this:
main =
AID ATRIPDT ACD ACAR CY1 CY2 OID OTRIPDT OCD BCAR DELMN
0 10/30/2018 AA XX22 LAS LAX 300 10/30/2018 BB ZZ1 21
0 10/30/2018 AA XX22 LAS LAX 544 10/30/2018 CC T09 36
0 10/30/2018 AA XX22 LAS LAX 755 10/30/2018 BB KLQ 57
0 10/30/2018 AA XX22 LAS LAX 912 10/30/2018 DD 75Q 5
1 10/30/2018 AA P700 LAS LAX 390 10/30/2018 BB MNZ 13
1 10/30/2018 AA P700 LAS LAX 603 10/30/2018 BB JJ1 30
However, the last step is to group by AID and select only one record for each OCD which should be the minimum value of DELMN.
In this case I am looking for this as a result:
AID ATRIPDT ACD ACAR CY1 CY2 OID OTRIPDT OCD BCAR DELMN
0 10/30/2018 AA XX22 LAS LAX 300 10/30/2018 BB ZZ1 21
0 10/30/2018 AA XX22 LAS LAX 544 10/30/2018 CC T09 36
0 10/30/2018 AA XX22 LAS LAX 912 10/30/2018 DD 75Q 5
1 10/30/2018 AA P700 LAS LAX 390 10/30/2018 BB MNZ 13
I tried this
with main as
(
<complex query that returns main table>
)
select * from main
where DELMN = (select min(DELMN) from main as b where b.OCD=main.OCD
which returns a total of three records so I am not setting up the grouping correctly. Am brain drained so not sure what else to try.

Answer 1

You want one row per AID+OCD value, so you'll want something like:
WITH main AS
(
<complex query that returns main table>
)
SELECT *
FROM main
WHERE DELMN = (SELECT MIN(DELMN)
FROM main AS b
WHERE b.OCD=main.OCD AND b.AID = main.AID)
GROUP BY AID, OCD
It won't be a very efficient query, but should work. It can be more efficient by JOINing to a query that pulls the minimum DELMN group by AID and OCD (rather than using a sub-select that runs for every row). That way, it only needs to scan those tables once. Don't worry about that unless you have LOTS of rows, which causes it to slow down.