Delete child records if the count exceeds 10 - mysql

Question

I have a parent-child relation for the following tables:
CREATE TABLE `pages` (
id INT NOT NULL AUTO_INCREMENT,
name VARCHAR(100) NULL,
PRIMARY KEY ( id )
)
CREATE TABLE `pageObjects` (
id INT NOT NULL AUTO_INCREMENT,
object TEXT NULL,
lastChanged TIMESTAMP on update CURRENT_TIMESTAMP NOT NULL,
fkPageId int NOT NULL,
PRIMARY KEY ( id )
)
The pages have a one:many relation with pageObjects.
Whenever the pageObjects records connected to a single page exceed 10, all records that are edited furthest in the past and exceeding the 10 must be deleted.
I wanted to do this in a single query, but I can't seem to figure this out...
This is how far I've gotten:
DELETE
FROM pageObjects
WHERE id NOT IN (
SELECT po.id, po.fkPageId FROM (
SELECT objects.fkPageId FROM (
SELECT COUNT(*) as count, fkPageId
FROM pageObjects
GROUP BY fkPageId
) objects
WHERE count > 10
) AS page
JOIN pageObjects po
ON page.fkPageId = po.fkPageId
AND po.lastChanged < (
SELECT MIN(lastChanged )
FROM pageObjects
WHERE fkPageId = po.fkPageId
GROUP BY fkPageId
ORDER BY lastChanged DESC
LIMIT 10
)
)
Sadly, the LIMIT bit in the bottom sub-query is not working the way I want to, because the MIN() function should be applied AFTER the LIMIT is applied.
So I tried that:
DELETE
FROM pageObjects
WHERE id NOT IN (
SELECT po.id, po.fkPageId FROM (
SELECT objects.fkPageId FROM (
SELECT COUNT(*) as count, fkPageId
FROM pageObjects
GROUP BY fkPageId
) objects
WHERE count > 10
) AS page
JOIN pageObjects po
ON page.fkPageId = po.fkPageId
AND po.lastChanged < (
SELECT MIN(lastChanged)
FROM (
SELECT lastChanged
FROM pageObjects
WHERE fkPageId = po.fkPageId
GROUP BY fkPageId
ORDER BY lastChanged DESC
LIMIT 10
)
)
)
But this is not possible, because the po.fkPageId is not available in the sub-query of the sub-query.
Is there any way to do this like this?

Answer 1

You can do this quite simply by counting the number of later entries for each id:
DELETE FROM pageObjects
WHERE id IN (
SELECT id FROM pageObjects po
WHERE (
SELECT count(id)
FROM pageObjects po2
WHERE po2.fkPageId = po.fkPageId
AND po2.lastChanged > po.lastChanged
) > 10
)
Check out what the select returns here:
http://www.sqlfiddle.com/#!9/f5218f/1/0