update table with data from other table in remote oracle db
I did it by:
creating dblink from db A to DB B
and using : merge into Y y using select X.columns from X@dblink x on (x.idX=y.idY)
when matched then update set
y.columns=x.columns --here ids are not included
when not matched then 
insert (y.columns) values(x.columns) --ids are included
x.colums and y.colums mean shared columns