Count number of unique values

Question

If I have three columns:

orderNumber, name, email

and I would like to count how many unique emails are in the table how would I go about do

Answer 1

The accepted soultion doesn't work for me - it returns a "1" for each unique email address in the table.

This is what I had to do to get the info I needed:

select email, count(email) AS total from sysAccessLog group by email order by total desc

Which returns a list of email addresses and the number of occurrences.