SQL how percent totals from two tables change over time - mysql

Question

Hi there I have a question regarding SQL structure. I have some of it figured out but I cant get the rest.
USERS TABLE
user OS_signup
1 Mobile
2 Windows
3 Mac
4 Mobile
5 Windows
DUNGEON TABLE
user dungeon progress status OS_completed deaths
1 Dungeon 1 1 finished Windows 0
1 Dungeon 1 2 incomplete Windows 0
2 Dungeon 2 1 finished Windows 1
3 Dungeon 2 1 finished Mac 1
3 Dungeon 1 2 finished Mac 3
3 Dungeon 3 3 incomplete Mac 0
4 Dungeon 1 1 finished Mobile 1
5 Dungeon 1 1 incomplete Windows 5
Which operating system is most popular when comparing the percent of users that completed the first level of progress of the first dungeon vs. users who have an account on the game?
I have this query
SELECT OS_signup, count(*) AS count_total
FROM users
GROUP BY OS_signup
and this one
SELECT OS_completed, count(*) AS count_completed
FROM dungeons
WHERE dungeon = "Dungeon 1" AND progress >=1 AND status = "finished"
GROUP BY OS_completed
I obviously get two tables, but I want to write a query that outputs a combined table so that I get one table that looks like this:
OS percent-done
Mobile 0.5
Windows 0.5
Mac 1
How can I write a query to achieve a table like the above?
Thank you!

Answer 1

for MySQL it could be something like this:
SELECT OS_signup, count(*) AS count_total, COUNT(tmp.user_id) as count_completed, COUNT(tmp.user_id) / COUNT(*) as percent
FROM users
LEFT JOIN (
SELECT user_id
FROM dungeons
WHERE dungeon = 'Dungeon 1' AND progress >= 1 AND status = 'finished'
GROUP BY user_id
) tmp ON tmp.user_id = users.id
GROUP BY OS_signup

Answer 2

Just join the results of these two queries together:
WITH total(OS, count_total) AS (
SELECT OS_signup, count(*)
FROM users
GROUP BY OS_signup
),
completed(OS, count_completed) AS (
SELECT OS_completed, count(*)
FROM dungeons
WHERE dungeon = 'Dungeon 1'
AND progress >= 1
AND status = 'finished'
GROUP BY OS_completed
)
SELECT OS,
count_total,
count_completed,
CAST(count_completed AS FLOAT) / count_total AS percent
FROM total
JOIN completed USING (OS)
ORDER BY ...;
(MySQL does not have common table expressions; you'd have to use views or subqueries instead.)