Question

I would like to merge these 2 queries to retrieve my datas in a view :

QUERY 1 :

    $query = $this->db->query('SELECT ft_upload_data.*, ft_categories.*, ft_categories.category_name
    FROM ft_upload_data
    LEFT JOIN assigned_categories ON assigned_categories.ft_upload_data_id = ft_upload_data.post_id
    LEFT JOIN ft_categories ON ft_categories.cat_id = assigned_categories.ft_categories_id
    ORDER BY ft_upload_data.rank ASC
    ');

    return $query->result();

QUERY 2 :

    $query2 = $this->db->query('SELECT a.post_id, 
    COUNT(*) AS num_comments
    FROM ft_upload_data a
    JOIN ft_comments c ON c.post_id = a.post_id
    GROUP BY a.post_id');

    return $query2->result();

I can’t figure it out :/ Any ideas to trick this?

Thanks !

Answer 1

The simplest (but not necessarily the most efficient) way would be to do it in an in-line query:

SELECT ft_upload_data.*, ft_categories.*,
       (SELECT COUNT(*) 
        FROM ft_comments c 
        where c.post_id = ft_upload_data.post_id) AS num_comments
FROM ft_upload_data
LEFT JOIN assigned_categories 
       ON assigned_categories.ft_upload_data_id = ft_upload_data.post_id
LEFT JOIN ft_categories 
       ON ft_categories.cat_id = assigned_categories.ft_categories_id
ORDER BY ft_upload_data.rank ASC

A more efficient way would be to join to the ft_comments table and group by post_id (assuming that this uniquely identifies ft_upload_data rows), like so:

SELECT ft_upload_data.post_id,
       /* include the maximum of each required field from ft_upload_data and 
          ft_categories here, with appropriate aliases */
       COUNT(*) AS num_comments
FROM ft_upload_data
LEFT JOIN assigned_categories 
       ON assigned_categories.ft_upload_data_id = ft_upload_data.post_id
LEFT JOIN ft_categories 
       ON ft_categories.cat_id = assigned_categories.ft_categories_id
LEFT JOIN ft_comments c 
       on  c.post_id = ft_upload_data.post_id
GROUP BY ft_upload_data.post_id
ORDER BY max(ft_upload_data.rank) ASC