thanks for responding.
I am writing like:
SELECT "customer" as "custM", "month" as "monthM", "country" as "countryM", "cost" as "costM"
FROM "mytable" as "M"
inner join
(
SELECT "customer" as "custS", "month" as "monthS", MIN("costSUM") AS "costMIN"
FROM
(SELECT distinct "customer", "country", "month", sum("cost") as "costSUM" FROM "mytable"
group by "customer", "country", "month")
group by "customer","month"
) as "S"
on "M"."customer" = "S"."custS" AND "M"."month" = "S"."monthS" AND "M"."cost"= "S"."costMIN"
this gives me result:
c001 US 201506 -100 c001 DK 201506 -100 c001 FR 201507 -200
but i need like:
c001 DK 201506 -100 c001 FR 201507 -200
OR
c001 US 201506 -100 c001 FR 201507 -200
how can i further enhance this SQL or should I write it in totally different way?
thanks