mysql - SQL 查询左连接问题

Question

我有两个表:users 和 userlogs

table1
----------
id | name
----------
1 | A
2 | B
3 | C
4 | D


table2
----------
user_id | date
----------
1 | 2015-12-17
2 | 2015-12-18
3 | 2015-12-19
4 | 2015-12-20

如果我对所选日期执行 LEFT JOIN，它只会提供表 2 中存在的数据。

SELECT r.user_id, count(r.user_id) as count
FROM table1 a LEFT OUTER JOIN table2 r ON ( r.user_id = a.id )
WHERE r.created_at BETWEEN '2015-12-17' AND '2015-12-19'
GROUP BY a.id

我得到以下信息

Result
----------
user_id | count
----------
1 | 1
2 | 1
3 | 1

我需要如下内容:

Result
----------
user_id | count
----------
1 | 1
2 | 1
3 | 1
4 | 0

我尝试了很多不同的方法，但都没有成功。

Answer 1

尝试将过滤条件移动到左连接中。

SELECT 
   a.id, 
   count(r.user_id) as count
FROM table1 a 
LEFT OUTER JOIN table2 r ON r.user_id = a.id AND 
                            r.created_at BETWEEN '2015-12-17' AND '2015-12-19'
GROUP BY a.id