MySQL加入并获取所有关系，即使为0

Question

我有两张 table 。一个保存所有可用的奖杯，一个保存用户和奖杯之间的关系。

trophy
--------------------------------------
| trophy_id | name                   |
--------------------------------------
| 1         | kill 100 people        |
| 2         | kill 200 people        |
| 3         | fly 5000 feet upwards  |
| 4         | fly into a mountain    |
--------------------------------------

earned_trophys
------------------------------------------
| earned_trophy_id | trophy_id | user_id |
------------------------------------------
| 1                | 1         | 3       |
| 2                | 1         | 2       |
| 3                | 3         | 4       |
| 4                | 2         | 1       |
| 5                | 3         | 1       |
------------------------------------------

例如 用户 1 赢得了杀死 100 人和杀死 200 人的奖杯。

我想要一个显示如下内容的查询:

for user 1
-----------------------------
| kill 100 people       | 1 |
| kill 200 people       | 1 |
| fly 5000 feet upwards | 0 |
| fly into a mountain   | 0 |
-----------------------------

这是我试过的:

select
    trophy.name,
    earned_trophys.user_id,  
    count(user_id) as temp
from
    trophy
left join
    earned_trophys
on
    trophy.trophy_id = earned_trophys.trophy_id
where
    earned_trophys.user_id = 1
group by
    name

但我只得到用户得到的结果，我想要 temp = 0 行。 是否可以在一个查询中执行此操作？

Answer 1

要使左连接生效，您需要将条件 earned_trophys.user_id = 1 移动到 on 子句中，而不是 where 中。

select
    trophy.name,
    earned_trophys.user_id,  
    count(user_id) as temp
from
    trophy
left join
    earned_trophys
on
    trophy.trophy_id = earned_trophys.trophy_id and earned_trophys.user_id = 1
group by
    name