mysql填写列中每个特定值的缺失日期

Question

我正计划在subchannel和l_events之间的2013-10-01表的2014-03-31列中计算事件数量，并按特定{{1}进行分组}，subchannel和year。

现在我的结果如下：

month

我希望我的结果包含每个特定子通道的行，其中当月没有发生任何事件。如下所示：

year    month   subchannel      count(*)
2013      10    creativemornings    1
2014       3    creativemornings    2
2013      11    founderinstitute    1

我尝试将我的查询加入我的日历表（其中包含所有相关日期的日期时间列），但它不起作用。有什么想法吗？

year    month   subchannel      count(*)
2013      10    creativemornings    1
2013      11    creativemornings    0
2013      12    creativemornings    0
2014       1    creativemornings    0
2014       2    creativemornings    0
2014       3    creativemornings    2
2013      10    founderinstitute    0
2013      11    founderinstitute    1
2013      12    founderinstitute    0
2014       1    founderinstitute    0
2014       2    founderinstitute    0
2014       3    founderinstitute    0

Answer 1

这样做。它创建子通道列表和日历表的笛卡尔积，并将l_events表LEFT JOIN连接到该结果集。

SELECT  
    year(c.datefield) as year,
    month(c.datefield) as month,
    s.subchannel,
    count(l.created)
FROM db.calendar c
    CROSS JOIN (select distinct subchannel from l_events) s
    LEFT JOIN db.l_events l
        ON (date(l.created) = c.datefield)
        AND l.subchannel = s.subchannel
Where c.datefield between '2013-10-01' and '2014-03-31' 
group by
    s.subchannel,
    year(c.created), 
    month(.created)
order by
    s.subchannel,
    year(c.created), 
    month(.created)
    ;