For that you'll need to know the database design/structure. One method is to make multiple inner joins between tables. Second way, is to "suppress duplicates". But be warned that supressing duplicates doesn't mean your count/sum functions will be correct. It will still add all double records. See "3 step formula" on the net on how to avoid this.
But the first question is: why are multiple entries written. From there, see if there's really no correct way to set the joins.