What does this query mean ?

Hello,
I am browsing the code of Invision Board v. 1.2 as I need to add some fileds to it.
So there is a Query to DB, that selects some fields, and that are used in Topics (Avatar, Post Count etc). I need that this query selected some other fileds from other table, but first I must understand how it works...
Heres the query:

$DB->query( "SELECT p.*,
m.id,m.name,m.mgroup,m.email,m.joined,m.avatar,m.a vatar_size,m.posts,m.aim_name,m.icq_number,
m.signature, m.website,m.yahoo,m.integ_msg,m.title,m.hide_email ,m.msnname, m.warn_level, m.warn_lastwarn,
g.g_id, g.g_title, g.g_icon, g.g_dohtml $join_get_fields
FROM ibf_posts p
LEFT JOIN ibf_members m ON (p.author_id=m.id)
LEFT JOIN ibf_groups g ON (g.g_id=m.mgroup)
$join_profile_query
WHERE p.topic_id=".$this->topic['tid']." and p.queued != 1
ORDER BY p.pid LIMIT $first, ".$ibforums->vars['display_max_posts']);

Heres the ibf_posts and ibf_members table structure:

mysql> describe ibf_posts;
+-------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+----------------+
| pid | int(10) | | PRI | NULL | auto_increment |
| append_edit | tinyint(1) | YES | | 0 | |
| edit_time | int(10) | YES | | NULL | |
| author_id | mediumint(8) | | MUL | 0 | |
| author_name | varchar(32) | YES | | NULL | |
| use_sig | tinyint(1) | | | 0 | |
| use_emo | tinyint(1) | | | 0 | |
| ip_address | varchar(16) | | | | |
| post_date | int(10) | YES | | NULL | |
| icon_id | smallint(3) | YES | | NULL | |
| post | text | YES | MUL | NULL | |
| queued | tinyint(1) | YES | | NULL | |
| topic_id | int(10) | | MUL | 0 | |
| forum_id | smallint(5) | | MUL | 0 | |
| attach_id | varchar(64) | YES | | NULL | |
| attach_hits | int(10) | YES | | NULL | |
| attach_type | varchar(128) | YES | | NULL | |
| attach_file | varchar(255) | YES | | NULL | |
| post_title | varchar(255) | YES | | NULL | |
| new_topic | tinyint(1) | YES | | 0 | |
| edit_name | varchar(255) | YES | | NULL | |
+-------------+--------------+------+-----+---------+----------------+
21 rows in set (0.00 sec)

mysql> describe ibf_members;
+-------------------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+-----------------------+------+-----+---------+-------+
| id | mediumint(8) | | PRI | 0 | |
| name | varchar(255) | | MUL | | |
| mgroup | smallint(3) | | MUL | 0 | |
| password | varchar(255) | | | | |
| email | varchar(255) | | | | |
| joined | int(10) | | | 0 | |
| ip_address | varchar(16) | | | | |
| avatar | varchar(128) | YES | | NULL | |
| avatar_size | varchar(9) | YES | | NULL | |
| posts | mediumint(7) | YES | | 0 | |
| aim_name | varchar(40) | YES | | NULL | |
| icq_number | varchar(40) | YES | | NULL | |
| location | varchar(128) | YES | | NULL | |
| signature | text | YES | | NULL | |
| website | varchar(70) | YES | | NULL | |
| yahoo | varchar(32) | YES | | NULL | |
| title | varchar(64) | YES | | NULL | |
| allow_admin_mails | tinyint(1) | YES | | NULL | |
| time_offset | varchar(10) | YES | | NULL | |
| interests | text | YES | | NULL | |
| hide_email | varchar(8) | YES | | NULL | |
| email_pm | tinyint(1) | YES | | NULL | |
| email_full | tinyint(1) | YES | | NULL | |
| skin | smallint(5) | YES | | NULL | |
| warn_level | int(10) | YES | | NULL | |
| warn_lastwarn | int(10) | | | 0 | |
| language | varchar(32) | YES | | NULL | |
| msnname | varchar(64) | YES | | NULL | |
| last_post | int(10) | YES | | NULL | |
| restrict_post | varchar(100) | | | 0 | |
| view_sigs | tinyint(1) | YES | | 1 | |
| view_img | tinyint(1) | YES | | 1 | |
| view_avs | tinyint(1) | YES | | 1 | |
| view_pop | tinyint(1) | YES | | 1 | |
| bday_day | int(2) | YES | MUL | NULL | |
| bday_month | int(2) | YES | MUL | NULL | |
| bday_year | int(4) | YES | | NULL | |
| new_msg | tinyint(2) | YES | | NULL | |
| msg_from_id | mediumint(8) | YES | | NULL | |
| msg_msg_id | int(10) | YES | | NULL | |
| msg_total | smallint(5) | YES | | NULL | |
| vdirs | text | YES | | NULL | |
| show_popup | tinyint(1) | YES | | NULL | |
| misc | varchar(128) | YES | | NULL | |
| last_visit | int(10) | YES | | 0 | |
| last_activity | int(10) | YES | | 0 | |
| dst_in_use | tinyint(1) | YES | | 0 | |
| view_prefs | varchar(64) | YES | | -1&-1 | |
| coppa_user | tinyint(1) | YES | | 0 | |
| mod_posts | varchar(100) | | | 0 | |
| auto_track | tinyint(1) | YES | | 0 | |
| org_perm_id | varchar(255) | YES | | | |
| org_supmod | tinyint(1) | YES | | 0 | |
| integ_msg | varchar(250) | YES | | | |
| temp_ban | varchar(100) | YES | | NULL | |
| clanid | mediumint(8) unsigned | | | 0 | |
| clanname | varchar(20) | | | 0 | |
| wins | mediumint(8) unsigned | | | 0 | |
| losses | mediumint(8) | | | 0 | |
| tcpoints | mediumint(8) unsigned | | | 0 | |
| streak | mediumint(8) unsigned | | | 0 | |
| totalgames | mediumint(8) unsigned | | | 0 | |
| lastgame | varchar(30) | | | 0 | |
+-------------------+-----------------------+------+-----+---------+-------+
63 rows in set (0.00 sec)

Why m.X(m.id,m.name) are used in this query ? What does p. , m. and g. mean ?
And what exactly does LEFT JOIN ibf_members m ON (p.author_id=m.id) do ?
I would be thankfull for any information you can provide,
CZealot

I'm not sure I understand what you are asking. If you're wondering why m.id, m.name, etc. are being selected, it's presumably because those values are used in the page.



These are all table aliases.
p = ibf_posts
m = ibf_members
g = ibf_groups



This includes a row of data (if it exists) from the ibf_members table. The row is the one where the id column of ibf_members (m.id) is the same as the author_id column in the ibf_posts table (p.author_id). This also assigns the alias "m" to the ibf_members table.

I suggest you get a book about SQL.