Question

I’m struggling with a join. Basically I want the tags results from my query to be in a single row.

Below are my tables:

• cover
• category
• cover_tag
• tag

The query returns the cover, category, and all tags for that category. NULL results in the tags are allowed, this is so I get all covers regardless if there are no tags added to it.

In the database I have 2 rows in the covers. The 1st cover has 3 tags, the 2nd cover has no tags. When running the query below I get 4 rows. 3 of them are the 1st cover, with a different tag, the 4th is the row without any tags.

I basically want 2 results with all the tags for each cover within the one row. Is this possible?

SELECT * 
FROM cover
JOIN category ON cover.category_id = category.id
LEFT OUTER JOIN cover_tag ON cover_tag.cover_id = cover.id
LEFT OUTER JOIN tag ON cover_tag.tag_id = tag.id

Data from phpMyAdmin

CREATE TABLE `category` (
  `id` int(9) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) NOT NULL,
  `slug` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;

INSERT INTO `category` VALUES(1, 'Cars', 'cars');
INSERT INTO `category` VALUES(2, 'Music', 'music');
INSERT INTO `category` VALUES(3, 'Abstract', 'abstract');

CREATE TABLE `cover` (
   `id` int(9) NOT NULL AUTO_INCREMENT,
   `category_id` int(9) NOT NULL,
   `title` varchar(255) NOT NULL,
   `slug` varchar(255) NOT NULL,
   `image` varchar(255) NOT NULL,
   `timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
   PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;

INSERT INTO `cover` VALUES(1, 1, 'Red Ferarri', 'red-ferarri', 'redferrari.jpg', '2011-12-20    23:48:11');
INSERT INTO `cover` VALUES(2, 1, 'Ford Focus ST', 'ford-focus-st', 'focuss.jpg', '2011-12-20 23:48:11');

CREATE TABLE `cover_tag` (
   `cover_id` int(9) NOT NULL,
   `tag_id` int(9) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

INSERT INTO `cover_tag` VALUES(1, 1);
INSERT INTO `cover_tag` VALUES(1, 2);
INSERT INTO `cover_tag` VALUES(1, 3);

CREATE TABLE `tag` (
  `id` int(9) NOT NULL AUTO_INCREMENT,
  `tag` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;

INSERT INTO `tag` VALUES(1, 'cars');
INSERT INTO `tag` VALUES(2, 'ferarri');
INSERT INTO `tag` VALUES(3, 'speed');

Answer 1

You can Concatenate them with GROUP_CONCAT with group by, something like this:

Select c.title, GROUP_CONCAT(t.tag SEPARATOR ', ')   
From cover c
Join cCategory ct on c.Category_Id = ct.id
LEFT OUTER JOIN cover_tag ctg ON c.Id = ctg.cover_id
LEFT OUTER JOIN tag t on ctg.tag_id = t.id
GROUP By c.title

This will give you the following:

   title          Tags
------------------------------------
Ford Focus ST   {NULL}
 Red Ferarri    cars, ferarri, speed