SELECT distinct area.shipcode, area.cruisenum, area.corenum, lat, long, waterdepth, (data/summe)*100 AS proz
FROM nandat, indproz_pt1, area, sample
WHERE sample.sample_id=indproz_pt1.sample_id
AND sample.sample_id=nandat.sample_id
AND area.area_id=sample.area_id
AND nandat.art=98
OR...