Question

在使用连接时我不是很好 - 所以我有一个表，我在计算满足特定条件的记录数，并按周返回这些计数。问题是，我需要那些零计数的周......我试图让它与左连接一起工作，但我正在努力...任何帮助赞赏:(邮票是一个日期时间字段）< / p>

查询：

SELECT week(stamp), count(*) AS mycount, YEAR(stamp) as theyear
FROM merges
WHERE completed = 1
AND stamp BETWEEN '2017/4/1 00:00:00' AND '2017/6/1 00:00:00' GROUP BY week(stamp)

返回：

week(stamp) | mycount | theyear

15 | 21 |2017

17 | 10 |2017

18 | 62 |2017

19 | 13 |2017

20 | 76 |2017

21 | 22 |2017

第16周缺席？我需要将此结果包含在上面，例如：

16 | 0 |2017

我感谢任何帮助 - 我知道这不是太难，但是当我读其他帖子的时候，我正试图理解如何做到这一点....

Answer 1

select weekValue, yearValue, coalesce(mycount,0)
from 

( SELECT distinct week(@startDate := @startDate + Interval 1 day) as weekValue,
year(@startDate := @startDate + Interval 1 day) as yearValue
FROM 
(select 0 union all select 1 union all select 3 union all select 4 
    union all select 5 union all select 6 union all select 6 union all select 7 
    union all select 8 union all select 9) t,
(select 0 union all select 1 union all select 3 
    union all select 4 union all select 5 union all select 6 
    union all select 6 union all select 7 union all select 8 union all select 9) t2,
(select 0 union all select 1 union all select 3 union all select 4 union all select 5 union all select 6 union all select 6 union all select 7 union all select 8 union all select 9) t3, 
(select 0 union all select 1 union all select 3 union all select 4 union all select 5 union all select 6 union all select 6 union all select 7 union all select 8 union all select 9) t4, 
(SELECT @startDate := '2017-03-31 00:00:00' ) as g

where 
@startDate < '2017-06-01 00:00:00' ) as generateWeekYear left join 

(SELECT week(stamp) as theweek, count(*) AS mycount, YEAR(stamp) as theyear
FROM merges
WHERE completed = 1
AND stamp BETWEEN '2017/4/1 00:00:00' AND '2017/6/1 00:00:00' GROUP BY week(stamp) ) as actualQuery

on  generateWeekYear.weekValue = actualQuery.theweek 
and generateWeekYear.yearValue = actualQuery.theyear

让我解释一下上面的问题，

子查询generateWeekYear =这用于根据两个输入生成不同的周和年让我们说startDate和endDate。 startDate应该比实际startDate少1天。因为如果你不这样做减去1天然后有可能松开一周。

现在您需要显示所有周和年。

现在你认为generateWeekYear会有更多的时间来执行，但事实并非如此。您可以检查这个generate an integer sequence in MySQL。

之后，您只需将上表与上表联系起来即可获得所需结果。

MySQL查询 - 转换为左连接以显示零结果？

1 个答案: