Group results after join?

问题

So, I have three tables. Movies, movies_genres and genres. I want to get a movie by its Id, and also join its genres in the result. I managed to join the results, but it doesn't display as i want it to. I'm not sure if what I'm asking is possible.

This is my query:

SELECT `movies`.*, GROUP_CONCAT(genres.id) AS genre_id, GROUP_CONCAT(genres.name) AS genre_name
FROM (`movies`)
INNER JOIN `movies_genres`
    ON `movies_genres`.`movie_id` = `movies`.`id`
INNER JOIN `genres`
    ON `genres`.`id` = `movies_genres`.`genre_id` WHERE `movies`.`id` = 19908
GROUP BY `movies`.`id`

The query was generated by Codeigniters Active Record class, here is the Codeigniter code if that helps:

$this->db->select('movies.*, GROUP_CONCAT(genres.id) AS genre_id, GROUP_CONCAT(genres.name) AS genre_name');
$this->db->from('movies');
$this->db->where('movies.id', $movie_id);
$this->db->join('movies_genres', 'movies_genres.movie_id = movies.id', 'inner');
$this->db->join('genres', 'genres.id = movies_genres.genre_id', 'inner');
$this->db->group_by('movies.id');

Here is the result i'm currently getting:

Array
(
    [id] => 19908
    [movie_title] => Zombieland
    [overview] => An easily spooked guy...
    [genre_id] => 28,12,35,27
    [genre_name] => Action,Adventure,Comedy,Horror
)

And this is what I want:

Array
(
    [id] => 19908
    [movie_title] => Zombieland
    [overview] => An easily spooked guy...
    [genres] => array(
        0 => array(
            'id' => 28,
            'name' => Action
        ),
        1 => array(
            'id' => 12,
            'name' => Adventure
        ),
        1 => array(
            'id' => 35,
            'name' => Comedy
        ),
        1 => array(
            'id' => 27,
            'name' => Horror
        )
    )
)

Is this possible, and if so, how?

回答1:

The query you listed will have n rows (where n = # of movies) whereas the query it seems you want will have many more rows (# of movie_genre's entries). You're probably better off leaving that query as it is, and doing some post processing.

Consider:

After you get it, just run your result (e.g. $result) array through something like:

foreach($result as &$row)
{
    // Split over commas
    $gi_elements = explode(',', $row['genre_id']);
    $gn_elements = explode(',', $row['genre_name']);

    // Build genre 
    $row['genre'] = array();
    for($i=0; $i<count($gi_elements); $i++)
    {
        $row['genre'][] = array('id' => $gi_elements[$i], 'name' => $gn_elements[$i]);
    }

     // Cleanup
     unset($row['genre_id']);
     unset($row['genre_name']);
}

Afterwards, $results will look exactly as you wish without extra database work.

EDIT: Fixed some typos.

来源：https://stackoverflow.com/questions/11209264/group-results-after-join

标签

php

mysql

codeigniter

join

group-by