MySQL查询LEFT JOIN意外结果

Question

带有左联接的mysql SELECT查询未产生我期望的结果。 我希望有人可以向我展示或指向正确的方向，

我正在尝试建立一个查询，在该查询中我从“用户”表中获取所有用户名，并从主表中获取他们在特定日期花费的所有时间的总和。 我使用了左联接，但没有得到预期的结果。

 SUM(m.time_spent) as sum_total_time
 FROM master as m
  LEFT OUTER JOIN users as u ON u.user_id = m.user_id
   WHERE m.date_created >= '2016-05-09'
  AND m.date_created <= '2016-05-13'
 GROUP BY name
 ORDER BY name

主表

master_id       user_id         time_spent               date_created
1                     1              40                   2016-05-01
2                     2             36                   2016-05-02
3                     3              56                   2016-05-03
4                     2             33                   2016-05-03
5                     1              32                   2016-05-05
nth                 nth       nth number                    nth date

用户表

user_id            first_name            last_name
1                     James                 Green
2                     Robert                 Cox 
3                    Andy                    Roger
etc                   etc                    etc

我希望输出结果应如下所示：

user_id       Name               sum_total_time

1               James Green          62
2               Robert Cox           69
3               Andy Roger           56
4               Brian Harper         0
5               Angel Lee            0
6               Andrew Martin        55
..... 
.....
Nth Name                             Nth value

Answer 1

您必须直接从主表中选择数据，按用户分组并计算总和。 然后，您可以将此结果与用户表结合起来以获取有关该用户的所有信息。

Answer 2

可能是日期转换问题。

 SUM(m.time_spent) as sum_total_time
 FROM master as m
  LEFT OUTER JOIN users as u ON u.user_id = m.user_id
   WHERE m.date_created >=STR_TO_DATE( '2016-05-09', '%Y-%m-%d)

和/或您也有不完整的sql

SUM(m.time_spent) as sum_total_time
 FROM master as m
  LEFT OUTER JOIN users as u ON u.user_id = m.user_id
   WHERE m.date_created >= '2016-05-09'
  AND m.date_created  // this condition don't match with nothing.. 
                      // could be you forgot a part 

更新1
如果您希望用户总数

   select u.id,   u.name, SUM(m.time_spent) as sum_total_time
   FROM master as m
   Inner  JOIN users as u ON u.user_id = m.user_id
   WHERE m.date_created >=STR_TO_DATE( '2016-05-09', '%Y-%m-%d)
   AND m.date_created <= =STR_TO_DATE('2016-05-13'', '%Y-%m-%d)
   Group by u.id