MySQL：计算多对多表中的实例

Question

I'm creating a small employment site and am wondering if this is possible in MySQL: I have 3 sample jobs and I want to show all users who applied to job_id = 1 who have an application status of 'pending' while showing the total number of other 'pending' and 'pending' + 'hired' applications each user has.

I've been trying to get my head around this but I'm having problems. Is this something MySQL can do?

users
+----+-------+
| ID |  name |
+----+-------+
|  1 | hanna |
|  2 |   bob |
|  3 |  rick |
+----+-------+

job
+--------+------------+
| job_id |   jobname  |
+--------+------------+
|      1 |    'waiter'|
|      2 |   'janitor'|
|      3 |      'cook'|
+--------+------------+

applications
+----------+---------+-----------+
| user_id  |  job_id |   status  | 
+----------+---------+-----------+
|        1 |       1 | 'pending' |
|        1 |       2 | 'pending' |
|        1 |       3 |  ' hired' |
|        2 |       1 | 'pending' |
|        3 |       1 | 'removed' |
+----------+---------+-----------+

My result set

+--------+---------+-----------+---------------+--------------------+
| job_id | user_id |   status  | count_pending | count_pendinghired |
+--------+---------+-----------+---------------+--------------------+
|      1 |       1 | 'pending' |             2 |                  3 |
|      1 |       2 | 'pending' |             1 |                  1 |
+--------+---------+-----------+---------------+--------------------+

Answer 1

The following query comes close to your suggested output. Note that it doesn't make sense to associate a single job_id with a given user, because a user may have multiple jobs. Likewise, it also doesn't make sense to associate a single status with a given user, since each record represents an aggregation of more than one status.

SELECT user_id,
       SUM(CASE WHEN status = 'pending' THEN 1 ELSE 0 END) AS count_pending,
       SUM(CASE WHEN status = 'pending' OR status = 'hired'
                    THEN 1 ELSE 0 END) AS count_pendinghired
FROM applications
GROUP BY user_id