Trying to do the right queries..

Question

I have a blog source I'm working on that uses the following tables:
TABLE posts:
+---------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| date | int(11) | NO | | NULL | |
| title | varchar(80) | NO | | NULL | |
| author | int(11) | NO | | NULL | |
| content | longtext | NO | | NULL | |
+---------+------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
TABLE tags:
+-------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| nav | tinyint(1) | NO | | NULL | |
| icon | varchar(40) | YES | | NULL | |
+-------+------------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)
TABLE tagpost:
+--------+------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+------------------+------+-----+---------+-------+
| tagid | int(10) unsigned | NO | | NULL | |
| postid | int(10) unsigned | NO | | NULL | |
+--------+------------------+------+-----+---------+-------+
tags and posts are pretty obvious; tagpost will be filled with multiple duplicates for normalization, basically. The issue I'm having is figuring out which sort of query I need to display posts properly. I'll need to fetch information from posts, tags, and users (for usernames).
I'm not sure where I need to start with this.. I think maybe subqueries or joining is what I need but I can't figure it out for myself.. any help?
I can post some of the code I'm using, but it's sort of hackish PHP.
Edit: Here's a graphical representation of my problem: http://bb.xieke.com/files/mysql-tables.png
Last edited by xelados (2008-10-15 19:19:44)

Answer 1

e_tank wrote:select posts.id, posts.title, posts.author, \
users.name as username, \
tagpost.tagid, \
tags.name \
from posts inner join users on posts.author = users.id \
inner join tagpost on posts.id = tagpost.postid \
inner join tags on tagpost.tagid = tags.id;
Unless you require that all posts have at least one tag, you should replace the last two INNER JOINs (or at least the second-to-last one -- I'm not certain what would happen in that case) with LEFT OUTER JOINs; as it stands, posts with no tags would be excluded from the results. (I assume an author is required, in which case the first INNER JOIN shouldn't cause a problem.)
Edit: I just verified in MySQL that -- indeed -- both of the last two joins should be LEFT OUTER JOINs (or, equivalently, LEFT JOINs).
Last edited by ssjlegendx (2008-10-16 01:04:32)