Вот:
create table POSITION
(
POS_DARR DATE not null,
POS_PTF_COD VARCHAR2(10) not null,
POS_VAL_COD VARCHAR2(15) not null,
POS_COURS NUMBER(17,6)
);

create table INTEGRATION
(
INT_DARR DATE not null
);

insert into INTEGRATION (INT_DARR)
values (to_date('20-07-2006', 'dd-mm-yyyy'));
insert into INTEGRATION (INT_DARR)
values (to_date('19-07-2006', 'dd-mm-yyyy'));
insert into INTEGRATION (INT_DARR)
values (to_date('18-07-2006', 'dd-mm-yyyy'));
insert into INTEGRATION (INT_DARR)
values (to_date('17-07-2006', 'dd-mm-yyyy'));

insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('20-07-2006', 'dd-mm-yyyy'), '1', '1', 10);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('19-07-2006', 'dd-mm-yyyy'), '1', '1', 10);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('18-07-2006', 'dd-mm-yyyy'), '1', '1', 12);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('17-07-2006', 'dd-mm-yyyy'), '1', '1', 10);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('20-07-2006', 'dd-mm-yyyy'), '1', '2', 10);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('19-07-2006', 'dd-mm-yyyy'), '1', '2', 10);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('18-07-2006', 'dd-mm-yyyy'), '1', '2', 10);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('17-07-2006', 'dd-mm-yyyy'), '1', '2', 10);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('20-07-2006', 'dd-mm-yyyy'), '1', '3', 10);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('19-07-2006', 'dd-mm-yyyy'), '1', '3', 12);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('18-07-2006', 'dd-mm-yyyy'), '1', '3', 12);
insert into POSITION (POS_DARR, POS_PTF_COD, POS_VAL_COD, POS_COURS)
values (to_date('17-07-2006', 'dd-mm-yyyy'), '1', '3', 10);

Запрос на 20/07/2006 должен выдать:

POS_PTF_COD POS_VAL_COD DATE_START
1 1 19/07/2006
1 2 17/07/2006

Пара (1, 3) в списке не должна фигурировать, поскольку курс в последний день изменился.