Question

说我有一张这样的桌子

| id | user_id | event_id | created_at |
|----|---------|----------|------------|
| 1  | 5       | 10       | 2015-01-01 |
| 2  | 6       | 7        | 2015-01-02 |
| 3  | 3       | 8        | 2015-01-01 |
| 4  | 5       | 9        | 2015-01-04 |
| 5  | 5       | 10       | 2015-01-02 |
| 6  | 6       | 1        | 2015-01-01 |

我希望能够为每个用户生成一个事件计数器。所以我的结果是：

| counter | user_id | event_id | created_at |
|---------|---------|----------|------------|
| 1       | 5       | 10       | 2015-01-01 |
| 1       | 6       | 7        | 2015-01-02 |
| 1       | 3       | 8        | 2015-01-01 |
| 2       | 5       | 9        | 2015-01-04 |
| 3       | 5       | 10       | 2015-01-02 |
| 2       | 6       | 1        | 2015-01-01 |

Answer 1

一个想法是自己加入表，group by复制其他RDBMS中可用的row_number() over..函数。

选中此Rextester Demo并查看第二个查询，了解inner join在这种情况下的工作原理。

    select  t1.user_id,
        t1.event_id,
        t1.created_at,
        count(*) as counter
from your_table t1
inner join your_table t2
on t1.user_id=t2.user_id 
    and t1.id>=t2.id
group by t1.user_id,
         t1.event_id,
         t1.created_at
order by t1.user_id,t1.event_id;

输出：

 +---------+----------+------------+---------+
| user_id | event_id | created_at | counter |
+---------+----------+------------+---------+
|       3 |        8 | 01-01-2015 |       1 |
|       5 |       10 | 01-01-2015 |       1 |
|       5 |       10 | 02-01-2015 |       3 |
|       5 |        9 | 04-01-2015 |       2 |
|       6 |        1 | 01-01-2015 |       2 |
|       6 |        7 | 02-01-2015 |       1 |
+---------+----------+------------+---------+

Answer 2

尝试以下方法：

select counter,
       xx.user_id,
       xx.event_id,
       xx.created_at
  from xx 
  join (select a.id,
               a.user_id,
               count(*) as counter 
          from xx as a 
          join xx as b 
            on a.user_id=b.user_id 
           and b.id<=a.id 
         group by 1,2) as counts 
         on xx.id=counts.id

使用联接为每个ID生成行，并在其下方为该用户提供所有其他较低的ID并对其进行计数。

Answer 3

试试这个：

子查询将有助于解决这个问题。

select  (select count(*) from user_event iue where iue.user_id  == oue.user_id) as counter,
    oue.user_id,
    oue.event_id,
    oue.created_at
from user_event oue

Answer 4

您可以尝试将变量用作表，将其与源表交叉连接，并在用户ID更改时重置。

SELECT @counter := CASE 
                     WHEN @user = user_id THEN @counter + 1 
                     ELSE 1 
                   END  AS counter, 
       @user := user_id AS user_id, 
       event_id, 
       created_at 
FROM   your_table m, 
       (SELECT @counter := 0, 
               @user := '') AS t 
ORDER  BY user_id;

我创建了一个演示here

每列行计数器

4 个答案: