Help with Join

Question

I need help with a join I think. Can't figure it out.

I have these tables:

Posts

`id` int(10) unsigned NOT NULL,
`title` varchar(140) DEFAULT NULL,
`text` text COLLATE utf8_unicode_ci

Posts tags

`post_id` int(10) unsigned NOT NULL,
`tag_id` int(10) unsigned NOT NULL

Tags

`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(40) DEFAULT NULL

If I want to loop out all the posts with the tag team-fortress-2 how would one do that? I can't figure it out.

$q = mysql_query("SELECT * FROM ... WHERE $get['tag']");
while($r = mysql_fetch_array($q)) {

Answer 1

SELECT p.*
FROM posts p
JOIN posttags pt ON pt.post_id = p.id
JOIN tags t ON pt.tag_id = t.id
WHERE t.name = 'team-fortress-2'

is the specific example. In PHP you'd do this:

$tag = mysql_real_escape_string($get['tag']);
$sql = <<<END
SELECT p.*
FROM posts p
JOIN posttags pt ON pt.post_id = p.id
JOIN tags t ON pt.tag_id = t.id
WHERE t.name = '$tag'
END;
$query = mysql_query($sql);
if (!$query) {
  $error = mysql_error();
  die("Error $error for query $sql");
}
...

Escaping the tag is really important, particularly if you are accepting it from user input in any way.

Answer 2

The SQL should look something like this:

select
   p.id, p.title, p.text
from
   Posts p
   inner join PostTags pt on pt.post_id = p.id
   inner join Tags t on t.id = pt.tag_id
where
   t.name = 'team-fortress-2'