The main Problem is the 'WHERE IN' on a Relation part, which multiply the found Rows.
For example where I added GROUP_CONCAT for a better view whats going on:
SELECT COUNT(*),
GROUP_CONCAT(sections.name SEPARATOR '; ')
FROM users
LEFT JOIN users_sections ON (users.id = users_sections.user_id)
LEFT JOIN sections ON (users_sections.section_id = sections.id)
GROUP BY users.id
Finds:
'2', 'Registered; admins'
'3', 'Registered; admins; dudes'
'1', 'Registered'
There are found 3 Rows, what is correct, but the Result is useless.
Now add the WHERE IN part:
SELECT COUNT(*),
GROUP_CONCAT(sections.name SEPARATOR '; ')
FROM users
LEFT JOIN users_sections ON (users.id = users_sections.user_id)
LEFT JOIN sections ON (users_sections.section_id = sections.id)
WHERE sections.id IN (2,3)
GROUP BY users.id
Finds:
'2', 'Registered; admins'
'2', 'Registered; admins'
'1', 'Registered'
Even correct but useless. I need one single '3' as COUNT result.
Ok then, lets remove the GROUP_CONCAT and ...pray
SELECT COUNT(*)
FROM users
LEFT JOIN users_sections ON (users.id = users_sections.user_id)
LEFT JOIN sections ON (users_sections.section_id = sections.id)
WHERE sections.id IN (2,3)
GROUP BY users.id
Find:
'2'
'2'
'1'
The same as before. Lets try this:
SELECT COUNT(*) > 0
...
Find:
'1'
'1'
'1'
Hey, that looks good! Lets try that (hopefully finally):
SELECT SUM(COUNT(*) > 0)
...
Find:
Invalid use of group function
So sad...
How can I get the Count for that, or is it impossible?
What you want to do (if i read correctly) is counting distinct user ids where a certain condition applies. I couldn't get the real question out of it, but I think you need it in the line of:
SELECT
COUNT( DISTINCT users.id)
FROM
users
LEFT JOIN users_sections ON (users.id = users_sections.user_id)
LEFT JOIN sections ON (users_sections.section_id = sections.id)
WHERE
sections.id IN (2,3)
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