MySQL count 2 columns in a row and join with another query - mysql

Question

I have a table visits like this:
+--------------+-------------+------+-----+---------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-------------+------+-----+---------------------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| vis_id | int(11) | NO | | NULL | |
| unit | int(11) | NO | | NULL | |
| time_in | timestamp | NO | | CURRENT_TIMESTAMP | |
| time_out | timestamp | NO | | 0000-00-00 00:00:00 | |
| in_username | varchar(16) | NO | | NULL | |
| out_username | varchar(16) | NO | | NULL | |
+--------------+-------------+------+-----+---------------------+----------------+
and a table users like this:
+------------+-------------+------+-----+---------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------------------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| fname | varchar(32) | NO | | NULL | |
| lname | varchar(32) | NO | | NULL | |
| date_added | timestamp | NO | | CURRENT_TIMESTAMP | |
| username | varchar(16) | NO | | NULL | |
| password | varchar(40) | NO | | NULL | |
| auth_level | int(1) | NO | | 1 | |
| last_login | timestamp | NO | | 0000-00-00 00:00:00 | |
+------------+-------------+------+-----+---------------------+----------------+
I want to be able to count how many times each user is in in_username AND out_username... The query I was using before looks like this:
select count(*) as "count", u.fname as "fname"
from visits v
inner join users as u on u.username = v.in_username
group by u.username order by u.fname
But that only returns how many in_username's there are... I'd like to have both in the same query if possible, so I could get results like this:
+----------+-----------+----------+
| count_in | count_out | fname |
+----------+-----------+----------+
| 118 | 224 | Bo |
| 27 | 64 | James |
| 147 | 138 | Jeremy |
| 23 | 37 | Jim |
| 182 | 172 | Robert |
| 120 | 158 | Tom |
+----------+-----------+----------+
Where count_in is how many times their username appears in visits.in_username, and count_out is how many times their username appears in visits.out_username
Everything I've tried with UNION seems to add the counts together, or removes rows for some reason. Any ideas?

Answer 1

Do a subquery to get each total, combine them with UNION, and then merge them with SUM().
SELECT SUM(count_in) count_in, SUM(count_out) count_out, fname
FROM (SELECT COUNT(*) count_in, 0 count_out, in_username fname
FROM visits v
GROUP BY fname
UNION
SELECT 0 count_in, COUNT(*) count_out, out_username fname
FROM visits v
GROUP BY fname) combined