Тестовая таблица:
CREATE TABLE "DBA"."testperiod" (
	"id" integer NOT NULL DEFAULT autoincrement,
	"d1" date NULL,
	"d2" date NULL,
	"v" integer NULL,
	"ls" integer NULL,
	CONSTRAINT "id" PRIMARY KEY ( "id" ));

Заполнил значениями:
delete testperiod;
begin
declare i integer;
set i= 1 ;
while i< 500000  loop
insert into testperiod(	"d1",	"d2",	"v" ,	"ls" )
select '2011-01-01','2011-01-05', 1 ,i
union
select '2011-01-06','2011-01-15', 1 ,i
union
select '2011-01-16','2011-01-25', 2 ,i
union
select '2011-01-26','2011-01-31', 1 ,i;
set i=i+ 1 
end loop;
end;

Запрос:
WITH recursive
   tree ( "d1",	"d2",	"v" ,	"ls",lv,dd1,dd2) 
   AS (SELECT "d1",	"d2",	"v" ,	"ls", 0 ,d1,d2
     FROM testperiod where d1='2011-01-01'
      UNION ALL 
      SELECT  V."d1",	v.d2,	V."v" ,	V."ls",t.lv+ 1 ,(if t.v=v.v then t.dd1 else v.d1 endif),v.d2
      FROM testperiod  
	  V  INNER JOIN tree t 
          ON  (t.ls = v.ls and t.d2+ 1 =v.d1 ))
select ls,dd1,max(dd2),v from tree
group by ls,dd1,v
order by dd1;