Question

我有以下表格：

members:
----------------------------------------------
| member_id | member_name | member_join_date |
----------------------------------------------  

events:
-------------------------
| event_id | event_name |
-------------------------

event_dates:
--------------------------------------
| event_id | event_date | event_week |
--------------------------------------

attendance:
------------------------------------------------------------
| member_id | event_id | attendance_date | attendance_week |
------------------------------------------------------------

所以我有成员在某个时间加入该组织，他们可能参加每周活动（其中发生的事件由event_dates表监控）

我想做的是让所有至少连续缺席3次的成员

我尽我所能，我认为我有查询的每一部分，但不知道如何将它们合并在一起。

获取他们可以参加的所有活动：

    SELECT
      m.member_id AS id,
      ed.event_id,
      ed.event_week
    FROM
      members AS m
      LEFT JOIN
        event_dates AS ed
        ON
          ed.event_date >= m.member_join_date

获取他们实际参加的所有活动：

    SELECT
      m.member_id AS id,
      a.event_id
    FROM
      members AS m
      LEFT JOIN
        attendance AS a
        ON
          a.member_id = m.member_id

如果我设法将两个查询合并为一个，那么可能是这个问题的答案：

Count of consecutive not null values

但这次我想计算NULL值

Answer 1

你可以尝试下面的内容：

select * from (select m.*,k.*, 
@rn := CASE WHEN bevent_id is null THEN @rn+1 ELSE 0 END AS rn
        from(
SELECT
      m.member_id AS id,
      ed.event_id  ,event_date  
    FROM
      members AS m
       left JOIN
        event_dates AS ed
        ON
          ed.event_date >= m.member_join_date) m
left join (SELECT
      m.member_id AS bid,
      a.event_id as bevent_id
    FROM
      members AS m
      LEFT JOIN
        attendance AS a
        ON
          a.member_id = m.member_id) k  on m.id=k.bid 
and m.event_id=k.bevent_id , (SELECT  @rn := 0) AS vars
order by m.id,m.event_date ) main
where rn>=3

使用您提供的两个查询，我执行左连接以比较两个查询的结果。为了跟踪成员是否缺席3连续事件，我使用@rn进行跟踪。

SQL FIDDLE here.

计算连接表中的连续空行

1 个答案: