difference between count(*) and count(columnName)

Question

I would like to know what are the differences between using:

SELECT email, COUNT( email ) AS total
FROM `newsletter`
GROUP BY email having total>1

or

SELECT count(*) as total, email 
FROM 'newsletter' 
GROUP BY email having total > 1

Both give same results but what else is counting count(*) than the emails?

Answer 1

There's at least one difference.

• They may return different results if email can contain NULL.

For more information, see this article.