How to INNER JOIN around a loop of tables - mysql

Question

I have four tables as follows:
CREATE TABLE IF NOT EXISTS `categories` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
PRIMARY KEY (`id`),
) ENGINE=MyISAM DEFAULT CHARSET=utf8 ;
CREATE TABLE IF NOT EXISTS `categories_friends` (
`category_id` int(10) unsigned NOT NULL,
`friend_id` int(10) unsigned NOT NULL,
UNIQUE KEY `category_id` (`friend_id`,`category_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
CREATE TABLE IF NOT EXISTS `friends` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`user_id` int(10) unsigned NOT NULL,
`friend_id` int(10) unsigned NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `user_id` (`user_id`,`friend_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 ;
CREATE TABLE IF NOT EXISTS `ratings` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`user_id` int(10) unsigned NOT NULL,
`category_id` int(10) unsigned NOT NULL,
`title` varchar(255) NOT NULL,
`description` text NOT NULL,
`rating` tinyint(2) unsigned NOT NULL,
`public` tinyint(1) NOT NULL DEFAULT '0',
`created` datetime NOT NULL,
PRIMARY KEY (`id`),
) ENGINE=MyISAM DEFAULT CHARSET=utf8 ;
I am trying to perform the following query on those tables:
SELECT *
FROM `favred`.`ratings` AS `Rating`
INNER JOIN `favred`.`friends` AS `JFriend`
ON (`JFriend`.`friend_id` = `Rating`.`user_id`)
INNER JOIN `favred`.`categories_friends` AS `JCategoriesFriend`
ON (`JCategoriesFriend`.`category_id` = `Rating`.`category_id`
AND `JCategoriesFriend`.`friend_id` = `JFriend`.`id`)
INNER JOIN `favred`.`categories` AS `JCategory`
ON (`JCategory`.`id` = `Rating`.`category_id`
AND `JCategory`.`id` = `JCategoriesFriend`.`category_id`)
WHERE `JFriend`.`user_id` = 1
AND `Rating`.`user_id` <> 1
AND `JCategory`.`id` IN (4, 14)
GROUP BY `Rating`.`id`
The query above is not working, as it returns no results (although there is data in the tables that should return), what I'm trying to do is to find all the Ratings that were not authored by me (ID:1), but were authored by my Friends, but only if I've selected to view a specific Category for that Friend, with the resulting set being filtered by a given set of specific Categories.
The INNER JOINs loop around through Rating --> Friend --> CategoriesFreind --> Category --> back to Rating.
If I remove the additional portion of the INNER JOIN's ON clauses as follows:
SELECT *
FROM `favred`.`ratings` AS `Rating`
INNER JOIN `favred`.`friends` AS `JFriend`
ON (`JFriend`.`friend_id` = `Rating`.`user_id`)
INNER JOIN `favred`.`categories_friends` AS `JCategoriesFriend`
ON (`JCategoriesFriend`.`friend_id` = `JFriend`.`id`)
INNER JOIN `favred`.`categories` AS `JCategory`
ON (`JCategory`.`id` = `JCategoriesFriend`.`category_id`)
WHERE `JFriend`.`user_id` = 1
AND `Rating`.`user_id` <> 1
AND `JCategory`.`id` IN (4, 14)
GROUP BY `Rating`.`id`
then the query will return results, but because the INNER JOIN joining the CategoriesFriend to the Rating is not being filtered by the 'JCategory'.'id' IN (4, 14) clause, it returns all Ratings by that friend instead of filtered as it should be.
Any suggestions on how to modify my query to get it to pull the filtered results?
And I'm using CakePHP, so a query that would fit into it's unique query format would be preferred although not required.

Answer 1

first ,why are you use the JFriend.id, does it mean something,or is it as the same as user_id?
try this one,the same logic but it's from top to bottom ,I feel:
SELECT * FROM categories as JCategory
INNER JOIN categories_friends as JCategoriesFriend ON JCategoriesFriend.category_id = JCategory.id
INNER JOIN friends AS JFriend ON JFriend.friend_id = JCategoriesFriend.friend_id
INNER JOIN ratings AS Rating ON Rating.user_id = JFriend.friend_id
WHERE JCategory.id IN (4,14) AND JFriend.user_id = 1 AND Rating.user_id <> 1 GROUP BY Rating.id
I got one result from all the data that I made for the testing.
if it does not work also,try make some correct data,maybe the data is not right...
the testing data below:
categories: id | name (14| 141414)
categories_friends: category_id| friend_id (14| 2)
friends: id | user_id | friend_id (4| 1| 2)
ratings: id | user_id | category_id | title (2| 2| 14 | 'haha')

Answer 2

So I wondered if the INNER JOINs were being a little too limiting and specific in their ON clauses. So I thought that maybe a LEFT JOIN would work better...
SELECT *
FROM `favred`.`ratings` AS `Rating`
INNER JOIN `favred`.`friends` AS `JFriend`
ON (`JFriend`.`friend_id` = `Rating`.`user_id`)
LEFT JOIN `favred`.`categories_friends` AS `JCategoriesFriend`
ON (`JCategoriesFriend`.`friend_id` = `JFriend`.`id`
AND `JCategoriesFriend`.`category_id` = `Rating`.`category_id`)
WHERE `JFriend`.`user_id` = 1
AND `JRatingsUser`.`id` IS NULL
AND `Rating`.`user_id` <> 1
GROUP BY `Rating`.`id`
That query worked for me.
I did away with linking to the categories table directly, and linked indirectly through the categories_friends table which sped up the query a little bit, and everything is working great.