Try this:
SELECT "STAT$DAN_2013".PERIOD, "STAT$DAN_2013".VESSEL_NAME AS "Skibsnavn", "STAT$DAN_2013".VOYAGE_NO AS "Voyage", SUM("STAT$DAN_2013".CREDIT_AMOUNT) - SUM("STAT$DAN_2013".DEBET_AMOUNT) AS "Total DKK", SUM("STAT$DAN_2013".TEUS) AS "Teus", (SUM("STAT$DAN_2013".CREDIT_AMOUNT) - SUM("STAT$DAN_2013".DEBET_AMOUNT)) / SUM("STAT$DAN_2013".TEUS) AS "Pr. teu"
FROM SCAN."STAT$DAN_2013" "STAT$DAN_2013"
WHERE "STAT$DAN_2013".DEPARTMENT=107 AND "STAT$DAN_2013".PERIOD<1307
GROUP BY rollup("STAT$DAN_2013".PERIOD, ("STAT$DAN_2013".VESSEL_NAME, "STAT$DAN_2013".VOYAGE_NO))
ORDER BY "STAT$DAN_2013".PERIOD, "STAT$DAN_2013".VESSEL_NAME, "STAT$DAN_2013".VOYAGE_NO;
I've added parentheses around the last two columns in the ROLLUP
.
I highly recommend this article by Tim Hall: Cube, Rollup and GROUPING functions