sql - how to get courses with module=5 - mysql

Question

I'm trying to get all courses which has only "module=5", any different course. As you can see below I have 4 courses, such as, course 2, 3, 4, 5. But just two of them has only "module=5", e.g. course 2, 5.
+----+--------+--------+
| id | course | module |
+----+--------+--------+
| 1 | 2 | 5 |
| 2 | 3 | 5 |
| 3 | 3 | 11 |
| 4 | 4 | 5 |
| 5 | 4 | 3 |
| 6 | 5 | 5 |
| 7 | 4 | 6 |
| 8 | 4 | 5 |
+----+--------+--------+
I've tryed do two queries, in the first I return all courses which has module=5 and in the second I return all courses which has module!=5, then I save in 2 files and execute the unix command diff to see the difference between both files.
save in a file all courses which has module=5:
SELECT DISTINCT fullname
FROM mdl_course
LEFT JOIN mdl_course_modules
ON mdl_course.id=mdl_course_modules.course
WHERE mdl_course_modules.module=5
into outfile '/tmp/forum';
save in file all courses which has module!=5:
SELECT DISTINCT fullname
FROM mdl_course
LEFT JOIN mdl_course_modules
ON mdl_course.id=mdl_course_modules.course
WHERE mdl_course_modules.module!=5
into outfile '/tmp/plus_forum';
Then, execute the difference:
$ diff forum plus_forum
But I'd like to return all courses which has only module=5 in only one query. Is it possible?

Answer 1

To make it simple let just solve the mdl_course_modules
SELECT course
FROM mdl_course_modules
GROUP BY course
HAVING SUM(module <> 5) = 0
AND SUM(module = 5) = 1 -- or >= 1

Answer 2

You can use a not in subquery to do this:
SELECT DISTINCT fullname
FROM mdl_course
LEFT JOIN mdl_course_modules
ON mdl_course.id=mdl_course_modules.course
WHERE mdl_course_modules.module=5
AND course.id not in (SELECT course
FROM mdl_course_modules
WHERE module <> 5)

Answer 3

One way to do this is to use the exists predicate with a correlated subquery.
select *
from mdl_course_modules t
where not exists (
select 1
from mdl_course_modules
where t.course = course -- reference the outer table
and module <> 5 -- and find rows that have any other module than 5
)
Sample SQL Fiddle
Since it's not completely clear what data is in what table you'll have to adjust the table and column names to suit your setup, but the concept should be clear.