Mysql 如何根据前几行的数据对表进行分组并获取行的结果

我有一个查找表，用于关联日期和与这些日期关联的人员：

id, user_id,date
1,1,2014-11-01
2,2,2014-11-01
3,1,2014-11-02
4,3,2014-11-02
5,1,2014-11-03

我可以按日期将其分组：

  SELECT    DATE_FORMAT(
                MIN(date),
                '%Y/%m/%d 00:00:00 GMT-0'
            ) AS date,
            COUNT(*) as count
    FROM    user_x_date
GROUP BY    ROUND(UNIX_TIMESTAMP(created_at) / 43200)

但是，如何获得以前显示过的唯一用户的数量呢？例如，这将是一个有效的结果：

unique, non-unique, date
2,0,2014-11-01
1,1,2014-11-02
0,1,2014-11-03

---

这可能不需要依赖脚本语言来跟踪这些数据吗？

我认为这个查询可以满足您的需要，至少它似乎可以为您有限的样本数据工作

其思想是使用相关子查询检查用户id是否出现在当前行日期之前的某个日期，然后执行一些基本算法来确定每个日期的唯一/非唯一用户数

请试一试

select 
  sum(u) - sum(n) as "unique", 
  sum(n) as "non-unique", 
  date 
from (
  select 
    date, 
    count(user_id) u, 
    case when exists (
      select 1 
      from Table1 i
      where i.user_id = o.user_id 
        and i.date < o.date
    ) then 1 else 0 
    end n
  from Table1 o
  group by date, user_id
) q
group by date
order by date;

---

我没有将id列包含在示例fiddle中，因为它不需要或不用于生成结果，也不会改变任何内容。

这是一个相关的问题：但是，如何获得以前显示的唯一用户的数量

计算人员第一次出现的时间，然后将其用于聚合：

SELECT date, count(*) as FirstVisit
FROM (SELECT user_id, MIN(date) as date
      FROM user_x_date
      GROUP BY user_id
     ) x
GROUP BY date;

SELECT v.date, v.NumVisits, COALESCE(fv.FirstVisit, 0) as NumFirstVisit
FROM (SELECT date, count(*) as NumVisits
      FROM user_x_date
      GROUP BY date
     ) v LEFT JOIN
     (SELECT date, count(*) as FirstVisit
      FROM (SELECT user_id, MIN(date) as date
            FROM user_x_date
            GROUP BY user_id
           ) x
      GROUP BY date
     ) fv
     ON v.date = fv.date;

然后，我会将其用作另一个聚合的子查询：

SELECT date, count(*) as FirstVisit
FROM (SELECT user_id, MIN(date) as date
      FROM user_x_date
      GROUP BY user_id
     ) x
GROUP BY date;

SELECT v.date, v.NumVisits, COALESCE(fv.FirstVisit, 0) as NumFirstVisit
FROM (SELECT date, count(*) as NumVisits
      FROM user_x_date
      GROUP BY date
     ) v LEFT JOIN
     (SELECT date, count(*) as FirstVisit
      FROM (SELECT user_id, MIN(date) as date
            FROM user_x_date
            GROUP BY user_id
           ) x
      GROUP BY date
     ) fv
     ON v.date = fv.date;