MySQL Joins where one value can be optional - mysql

Question

Situation
I have a database which heavily makes use of joins due to the various situations in which each entity is used. Here is a simplified diagram:
Goal
I would like to be able to get details of all modules and the "name" fields regardless of whether the "fk_chapter_id" within user_has_module is set or not.
In the case where "user_has_module.fk_chapter_id" is null, the system can return details of the module and then null chapter.
In the case where there is a user_has_module, I would like to get the status
Issue
Whenever I perform SQL statements, I get the results only partially returned. I.E. If I have 4 module records in total, two of which where the user has an entry in "user_has_module" returns the two records in full and then 2 null records for the other modules.
Update based on feedback, almost there
Now, the only problem is I get duplicates. Using some test data
SELECT DISTINCT
chapter_id,
chapter_name,
module_id,
module_name,
(null ) AS user_module_progress,
(SELECT COUNT(fk_chapter_id) FROM module_has_chapter WHERE fk_module_id = m.module_id) AS chapter_count
FROM
module as m
LEFT JOIN
module_has_chapter as mhc ON m.module_id = mhc.fk_module_id
LEFT JOIN
chapter as c ON mhc.fk_chapter_id = c.chapter_id
group by m.module_id
UNION
SELECT DISTINCT
chapter_id,
chapter_name,
module_id,
module_name,
user_module_progress,
(SELECT COUNT(fk_chapter_id) FROM module_has_chapter WHERE fk_module_id = m.module_id) AS chapter_count
FROM
module as m
LEFT JOIN
user_has_module as uhm ON m.module_id = uhm.fk_module_id
LEFT JOIN
user as u ON uhm.fk_user_id = u.user_id
LEFT JOIN
chapter as c ON uhm.fk_latest_chapter_id = c.chapter_id
WHERE u.user_id = 2
group by m.module_id;

Answer 1

I got there in the end but, not particularly happy about it. This works but, it's a bloody mess...Does anyone have a better solution please?
SELECT DISTINCT
(null) AS chapter_id,
(null) AS chapter_name,
module_id,
module_name,
(null ) AS user_module_progress,
(SELECT COUNT(fk_chapter_id) FROM module_has_chapter WHERE fk_module_id = m.module_id) AS chapter_count
FROM
module as m
LEFT JOIN
user_has_module as uhm ON m.module_id = uhm.fk_module_id
WHERE
uhm.fk_user_id IS NULL
UNION ALL
SELECT DISTINCT
chapter_id,
chapter_name,
module_id,
module_name,
user_module_progress,
(SELECT COUNT(fk_chapter_id) FROM module_has_chapter WHERE fk_module_id = m.module_id) AS chapter_count
FROM
module as m
LEFT JOIN
user_has_module as uhm ON m.module_id = uhm.fk_module_id
INNER JOIN
user as u ON uhm.fk_user_id = u.user_id
INNER JOIN
chapter as c ON uhm.fk_latest_chapter_id = c.chapter_id
WHERE
u.user_id = 2;