MySQL的填补了

Question

列

失踪日期为每个特定的价值我想数清我l_events表的日期2013-10-01和2014-03-31和组之间的subchannel列事件按特定subchannel，year和month的数量。

现在我的结果是这样的：

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

，我想我的结果包括在没有发生的事件发生当月每一个具体的子信道行。因此，像：

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 

我想加入我的查询到我的日历表（包括所有培训相关日期的日期时间列），但没有奏效。有什么想法吗？

SELECT 
     year(l.created) as year, 
     month(l.created) as month, 
     l.subchannel, 
     count(*) 

    FROM db.l_events l 

    right JOIN db.calendar c 
     ON (date(l.created) = c.datefield) 

    WHERE 
     l.created between '2013-10-01' and '2014-03-31' 

    group by 
     l.subchannel, 
     year(l.created), 
     month(l.created) 
     ; 

Answer 1

这样做。它会创建子通道列表和日历表的笛卡尔积，并且将l_events表联接到该结果集。

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) 
    ;