that are the defintion of the table

I will test your seuggestion as soon as I can

thanks a lot

iis_uu_diario_resume

Hora_iniciovarchar2551

Hora_finevarchar2551

paginasint41

hora_origenchar101

mes_origenchar101

dia_origenchar101

uuvarchar501

col018_dominiovarchar2551

uu_sessionvarchar501

uu_dia_castint41

uu_mes_castint41

all rows allow nulls

1UUvarchar501

0UUNumdecimal91

0UU_Sessionvarchar2551

0UU_SessionNumIdint40

0UU_SessionNumint41

0Dominiovarchar2551

0Dominio_generalvarchar501

0fechadatetime81

0Hora_iniciodatetime81

0Hora_finedatetime81

0Duracionint41

0Paginasint41

0RangoPaginasint41

0Hora_origenint41

0Dia_origenint41

0Mes_origenint41

0Caracteristicachar101

0Cardinalidadint41

all colums allow nulls except uu_sessionumid

Thanks for the counselling. I will apply it, but....

I made the test many times (5 or 6) one after another one: every of the two SELECT was always same time:...

thanks for the answers

1) the plans are the same

2) sure that changing the statement it works better but the point is. why there is such a big difference in performance...