Oracle Database Discussions

I have to execute a case insentitive search.
I created this index on a not null field:


create index indx_prova on
table (nlssort(campo, 'NLS_SORT=BINARY_CI'));


The select is:

select * from tabella where campo like 'A storage%'

This select should retrive 5 records:
A storage ring for crystalline beam studies
a storage ring for crystalline beam studies
A Storage Ring for Crystalline Beam Studies
A storage ring for crystalline beam studies
A storage ring for crystalline beam studies

Instead I got only 3 records:

A storage ring for crystalline beam studies
A storage ring for crystalline beam studies
A storage ring for crystalline beam studies

So The query isn't case insensitive.

I can't set nls_sort=BINARY_CI and nls_comp=LINGUISTIC at level session.

Is there a solution.
Am I doing something wrog?