mysql按列将2个表与一个公共组组合在一起

Question

我有 2 个带日期的表格，采用时间戳格式， 我要数一数每周总共有多少条记录...

...只需一个查询即可获得结果...

所以我会用例子更好地解释它：

2表，第一个：

table name: visitor

ID  | time  | ref     (now i put in fake timestamp in time column sorry)
--------------------
1   | 3455  | john
2   | 3566  | ted     (week 40)
3   | 8353  | ted     (week 38)
4   | 6673  | katy
5   | 6365  | ted     (week 40)
6   | 4444  | john
7   | 3555  | ted     (week 40)

和第二个（非常相似）：

table name: users

ID  | time  | ref     (now i put in fake timestamp in time column sorry)
--------------------
1   | 3455  | ted     (week 41)
2   | 3566  | ted     (week 42)
3   | 8353  | ted     (week 40)
4   | 6673  | katy
5   | 6365  | ted     (week 41)
6   | 4444  | john
7   | 3555  | ted     (week 38)
8   | 6789  | ted     (week 43)

我做这个查询，我得到这个结果：

SELECT WEEK(FROM_UNIXTIME(time)) AS week, COUNT( * ) AS tot
FROM visitor WHERE ref='ted' GROUP BY week

表格结果#1

week | tot
----------
38   |  1
40   |  3
43   |  1

我为第二张桌子做了一些：

SELECT WEEK(FROM_UNIXTIME(time)) AS week, COUNT( * ) AS totuser
FROM users WHERE ref='ted' GROUP BY week

表格结果#2

week | totuser
----------
38   |  1
40   |  1
41   |  2
42   |  1

但我只需要一个查询就可以得到这个结果：

week | tot | totusers
----------------------  (when both are 0 doent appear -like 39 for example-)
38   |  1  |   1
40   |  3  |   1
41   |  0  |   2
42   |  0  |   1
43   |  1  |   0

我知道我必须使用 LEFT JOIN、GROUP BY 和 IFNULL，但我总是做错事，我无法弄清楚。

按周顺序排列

感谢您的帮助。

Answer 1

从技术上讲，您想要的是full outer join，但 MySQL 不支持它。我使用union all 和group by 来解决这个问题：

SELECT weeek, SUM(visitors) as visitors, SUM(users) as users
FROM ((SELECT WEEK(FROM_UNIXTIME(time)) AS week, COUNT( * ) AS visitors, 0 as users
       FROM visitor
       WHERE ref='ted'
       GROUP BY week
      ) UNION ALL
      (SELECT WEEK(FROM_UNIXTIME(time)) AS week, 0, COUNT( * )
       FROM users
       WHERE ref ='ted'
       GROUP BY week
      )
     ) w
GROUP BY week
ORDER BY week;

注意：与您的数据一样，这仅包括访问者或用户的周数。如果您不想要周数，最好从一个包含您想要的所有周数的表格开始（某种日历表）。