ON DUPLICATE KEY: Ambiguous - php

Question

Following db structure:
Table cms_pages containing pages with id, name, title, etc.
Table cms_pagerows containing rows with a cms_page_id and rank
(Unique index over cms_page_id, rank)
The Pagerows are supposed to contain cols which in turn contain the... content.
I now want to insert a new pagerow into cms_pagerows on an existing page using php.
Ranks are not necessarily consecutive numbers because of the deletion of old pagerows.
For this, I have a function insertRowAt($page_name, $offset) with the following SQL:
INSERT INTO `cms_pagerows` (`cms_page_id`, `rank`)
SELECT `cms_pages`.`id`, `cms_pagerows`.`rank` + 1
FROM `cms_pages`, `cms_pagerows`
WHERE `cms_pages`.`name` = "'.$page_name.'"
AND `cms_pagerows`.`cms_page_id` = `cms_pages`.`id`
ORDER BY `rank` DESC
LIMIT 0, "'.$offset.'"
ON DUPLICATE KEY UPDATE `cms_pagerows`.`rank` = `cms_pagerows`.`rank` + 1
When trying to run it, I get the following error message: "Column 'cms_pagerows.rank' in field list is ambiguous"

Answer 1

The key is to always use table aliases to disambiguate the columns:
INSERT INTO `cms_pagerows`(`cms_page_id`, `rank`)
SELECT p.`id`, pr.`rank` + 1
FROM `cms_pages` p join
`cms_pagerows` pr
on pr.`cms_page_id` = p.`id`
WHERE p.`name` = "'.$page_name.'"
ORDER BY pr.`rank` DESC
LIMIT 0, "'.$offset.'"
ON DUPLICATE KEY UPDATE `rank` = pr.`rank` + 1;
You can also say:
ON DUPLICATE KEY UPDATE `rank` = VALUES(`rank`)
This works because the select is already going to insert the correct rank, so you can just use that value.

Answer 2

try this..
INSERT INTO `cms_pagerows` (`cms_page_id`, `rank`)
SELECT `cms_pages`.`id`, `cms_pagerows`.`rank` + 1 AS rank1
FROM `cms_pages`, `cms_pagerows`
WHERE `cms_pages`.`name` = "'.$page_name.'"
AND `cms_pagerows`.`cms_page_id` = `cms_pages`.`id`
ORDER BY rank1 DESC
LIMIT 0, "'.$offset.'"
ON DUPLICATE KEY UPDATE `rank` = rank1 + 1
two rank fields are conflicting because you are using same name... use AS keyword of mysql..