Parece que el problema es, como no y una vez mas, Microsoft:
"Re: Distinct count syntax?
Unfortunately, count distinct is simply not provided in Jet. You have to make
a nested query instead, where the first query groups by all the intended group
by fields plus the value in question, then the second includes just the
intended group by fields and includes a simple Count(*) in the Select list."
bytes.com/topic/access/answers/193528-di…count-syntax
Asi que resulta que para Access no hay ¿COUNT DISTINCT?
Que dificil es de creer esto, coño...
A ver asi:
SELECT COUNT (*) as Total
FROM (SELECT DISTINCT Fecha FROM Principal)
Aun no la he probado (cuando el nano duerma me pongo a ello), pero parece que la idea va a ser tal que esa... LOL!
un saludo