select a.cod_plaintiff, a.flastchild,a.slastchild, a.fnamechild, a.snamechild, b.cod_case, count(*)  from childs a, groups b, demandante c where a.cod_plaintiff=c.cod_plaintiff and b.cod_group=c.cod_group 
group by cod_case order by cod_case

select a.cod_plaintiff, a.flastnamep,a.slastnamep,firstnamep, b.cod_plaintiff, c.cod_case from demandante a, childs b, groups c where a.cod_plaintiff=b.cod_plaintiff and a.cod_group=c.cod_group and c.cod_group=2