Question

My Current Database Structure:

     `images`            `tags`             `images_tags`
 ________________    ______________    ________________________
| id | title     |  | id | name    |  | id | image_id | tag_id |
|----|-----------|  |----|---------|  |----|----------|--------|
|  1 | Ivysaur   |  |  1 | fire    |  |  1 |     2    |    1   | Charizard: fire
|  2 | Charizard |  |  2 | flying  |  |  2 |     2    |    2   | Charizard: flying
|  3 | Squirtle  |  |  3 | water   |  |  3 |     1    |    4   |   Ivysaur: grass
|  4 | Pidgey    |  |  4 | grass   |  |  4 |     4    |    2   |    Pidgey: flying
 ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯    ¯¯¯¯¯¯¯¯¯¯¯¯¯¯    ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

I want to output tags with their respective values (name).

if ($_GET["pokemon"] == "2") {
    // output Charizard's tags: fire, flying
}

But I am struggling at coming up with a proper query to do this. INNER JOIN is unfamiliar to me and an explanation on how it works would be very helpful.

Answer 1

Pokemon. LOL! xD

To output tags:

SELECT t.id, t.name
FROM tags AS t 
   INNER JOIN images_tags AS r ON r.tag_id =t.id
   INNER JOIN images AS i ON r.image_id =i.id
WHERE i.id ='2'

1. Select from the tags table and alias it as “t”
2. Join the third table (association) with the alias “r” and with r.tag_id =t.id
3. Join the images table with the alias “i” and with r.image_id =i.id
4. Finally sets the filter: i.id =’2′ (but will be mysql_real_escape_string($_GET['pokemon']) since you do not want SQL injection)

Now a shortcut:

if(isset($_GET['pokemon')) {
    $image_id = (int) $_GET['pokemon'];
    $r = mysql_query("SELECT t.* FROM tags t, tags_images r WHERE r.tag_id =t.id AND r.image_id ='$image_id'");
    while($tag = mysql_fetch_assoc($r)) {
        echo $tag['name'] . '<br />';
    }
}