Count unique rows mysql (stuck with count that returns non distinct values)

Question

I'm stuck, I tried to grab statistics from DB.

My query needs to return count of users that at least have 1 entry in connections table.

So I tried:

SELECT DISTINCT (u.id) AS total_has_atleast_one_word FROM users AS u
LEFT JOIN connections AS c
ON u.id = c.user_id
WHERE c.word_id IS NOT null;

This returns correct user_id, I've 3 rows with correct id which is all fine.

But when I do count(u.id) it returns 35 which instead should be 3. My understanding is it is counting non DISTINCT number of rows. So what should I do?

And as a last part of my question, how do I unite this with other stat queries of mine?

/*SELECT COUNT(u.id) AS total_users,
       sum(u.created < (NOW() - INTERVAL 7 DAY)) as total_seven_day_period,
       sum(u.verified = 1) as total_verified,
       sum(u.level = 3) as total_passed_tut,
       sum(u.avatar IS NOT null) as total_with_avatar,
       sum(u.privacy = 0) as total_private,
       sum(u.privacy = 2) as total_friends_only,
       sum(u.privacy = 3) as total_public,
       sum(u.sex = "F") as total_female,
       sum(u.sex = "M") as total_male
FROM users AS u;*/

Testing playground: http://www.sqlfiddle.com/#!2/c79a6/63

Answer 1

SELECT COUNT(DISTINCT user_id) FROM connections

Answer 2

for the first part :

/* user ids of those who have ever connected */
Select user_id from connections group by user_id

/* to get those who have connected after a particular date time ... */
Select user_id from connections group by user_id where connection_time > '2013-11-23' 

/* join with user table to get user details e.g. .. */   
Select u.name , u.address from user u
join on (Select user_id from connections group by user_id) c on c.user_id =u.user_id