Without a lot of information, I guess you could do something like this.

SELECT distinct BO.NMDOS,

CASE WHEN FT.FNO = MIN(FT.FNO) OVER(PARTITION BY BO.NMDOS) THEN bo.ETOTALDEB END AS ETOTALDEB ,

bo.tpdesc ,

bo.dataobra,

BO.NOME ,

BO.OBRANO,

ft.nmdoc,

FT.FNO,

CASE WHEN FT.NDOC<> 1

THEN 0

ELSE FT.ETTILIQ

END as etiliquido

FROM BO left JOIN BI ON bi.bostamp=bo.bostamp left JOIN FI ON fi.bistamp=bi.bistamp

left JOIN FT ON FT.FTSTAMP=FI.FTSTAMP WHERE BO.ndos='18' and bo.fechada=0

GROUP BY BO.NMDOS,bo.DATAOBRA,BO.NOME,BO.OBRANO,BI.OBRANO,FT.FNO,FT.ETTILIQ,bo.tpdesc ,ft.nmdoc,bo.ETOTALDEB,ft.ndoc

order by bo.DATAOBRA