sql - SQL-在每个用户第 n 次发生事件后返回行

Question

我正在使用 postgreSQL 8.0，并且我有一个带有 user_id、timestamp 和 event_id 的表。

如何在每个用户第 4 次出现 event_id = someID 后返回行（或行）？

|---------------------|--------------------|------------------|
|      user_id        |     timestamp      |     event_id     |
|---------------------|--------------------|------------------|
|          1          |  2020-04-02 12:00  |        11        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 13:00  |        11        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 14:00  |        99        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 15:00  |        11        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 16:00  |        11        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 17:00  |        11        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 17:00  |        11        |
|---------------------|--------------------|------------------|

即如果event_id = 11，我只想要上表中的最后一行。

Answer 1

您可以使用窗口函数：

select *
from (
    select t.*, row_number() over(partition by user_id, event_id order by timestamp) rn
    from mytable t
) t
where rn > 4

这是一个从结果中删除行号的小技巧：

select (t).*
from (
    select t, row_number() over(partition by user_id, event_id order by timestamp) rn
    from mytable t
) x
where rn > 4

Answer 2

您可以使用累积计数。此版本包括第 4 次出现：

select t.*
from (select t.*,
             count(*) filter (where event_id = 11) over (partition by user_id order by timestamp) as event_11_cnt
      from t
     ) t
where event_11_cnt >= 4;

长期以来filter，Postgres 语法一直是有效的，但您可以使用：

select t.*
from (select t.*,
             sum( (event_id = 11)::int ) over (partition by user_id order by timestamp) as event_11_cnt
      from t
     ) t
where event_11_cnt >= 4;

此版本不：

where event_11_cnt > 4 or (event_11_cnt = 4 and event_id <> 11)

另一种方法：

select t.*
from t
where t.timestamp > (select t2.timestamp
                     from t t2
                     where t2.user_id = t.user_id and
                           t2.event_id = 11
                     order by t2.timestamp
                     limit 1 offset 3
                    );

Answer 3

很抱歉询问这么旧版本的 Postgres，这是一个有效的答案：

WITH EventOrdered AS(
  SELECT 
    EventTypeId
    , UserId
    , Timestamp
    , ROW_NUMBER() OVER (PARTITION BY EventTypeId, UserId ORDER BY Timestamp ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) ROW_NO
  FROM Event),
FourthEvent AS (
  SELECT DISTINCT
    UserID
  , FIRST_VALUE(TimeStamp) OVER (PARTITION BY UserId ORDER BY Timestamp) FirstFourthEventTimestamp
  FROM EventOrdered
  WHERE ROW_NO = 4)
SELECT e.*
FROM Event e
JOIN FourthEvent ffe
  ON e.UserId = ffe.UserId
  AND e.Timestamp > ffe.FirstFourthEventTimestamp
ORDER BY e.UserId, e.Timestamp