select newcode,iname,max(iiname),max(iiiname)
from (select t1.newcode,iname,iiname,iiiname 
     from table1 t1,table2 t2,table3 t3 
     where t1.newcode=t2.newcode and t1.newcode=t3.newcode) t
group by newcode,iname;

select newcode,iname,min(iiname),min(iiiname)
from (select t1.newcode,iname,iiname,iiiname 
     from table1 t1,table2 t2,table3 t3 
     where t1.newcode=t2.newcode and t1.newcode=t3.newcode) t
group by newcode,iname;

------解决方案--------------------
SQL code
select t1.newcode, t1.iname, t2.iiname, t3.iiiname
from table1 t1 join (select newcode, min(iiname) from table2 group by newcode) t2 on t1.newcode=t2.newcode
    join (select newcode, min(iiiname) from table3 group by newcode) t3 on t1.newcode=t3.newcode