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 doing so?

A statement like:

SELECT count(email) FROM orders 

gives me the total count.

I tried SELECT DISTINCT count(email) FROM orders

but that does not seem to be giving me the numbers I am expecting.

Answer 1

use

SELECT count( DISTINCT(email) ) FROM orders 

Distinct provide unique email ids and then simply count them.

Answer 2

SELECT  count(DISTINCT(email)) FROM orders 

its different from your posting, since its filters out the duplicates before counting it