How can I change the format of a date in SQL Language?

If you want to retrieve the results stored in BDD with this format, in the selects you use to obtain the dates you can use this formatting. Surely there is some more efficient way, but hey, I leave it here:

select to_char(col_fecha, 'DD') || ' de ' ||to_char(col_fecha, 'MONTH') || ' del año ' || to_char(col_fecha, 'YYYY') 
from tabla;

If the field is nullable you will need to enter a CASE WHEN to control those specific cases.

Complex cases are not necessary, TO_CHAR can handle the format. You just need to pass the code of value NLS_DATE_LANGUAGE adequate. The accepted solution may not be the correct result (for the value of the month) if the NLS_DATE_LANGUAGE of the session is other than SPANISH

SELECT TO_CHAR(CAMPO_FECHA, 'DD "de" Month "del año" YYYY', 'NLS_DATE_LANGUAGE=SPANISH') FROM tabla;

Exit:

08 de Marzo del año 2018