Question

我被困住了，我试图从数据库中获取统计数据。

我的查询需要返回至少在连接表中有1个条目的用户数。

所以我试过了：

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;

这会返回正确的user_id，我有3行，ID正确，这一切都很好。

但是，当我计算（u.id）时，它返回35，而应该是3.我的理解是它计算非DISTINCT行数。那我该怎么办？

作为我问题的最后一部分，我如何将其与我的其他统计查询联合起来？

/*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;*/

测试游乐场：http://www.sqlfiddle.com/#!2/c79a6/63

Answer 1

SELECT COUNT(DISTINCT user_id) FROM connections

Answer 2

第一部分：

/* 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

计算唯一行mysql（卡住计数返回非不同的值）

2 个答案: