Contitionally structured and ordered MySQL query - php

Question

I have a table in a MySQL Database.
It is structured as such:
CREATE TABLE `wall` (
`wall_id` int(10) NOT NULL auto_increment,
`user_id` int(10) NOT NULL,
`wall_content` varchar(1024) NOT NULL,
`time_posted` varchar(64) NOT NULL,
`is_reply` int(10) NOT NULL,
PRIMARY KEY (`wall_id`)
) ENGINE=MyISAM
The column 'is_reply' will be the id of 'wall_id' to which it is a reply of. How would I structure a query to get all the rows based on an inner join of another table to cross reference the user_id, and to group the wall posts with the comments below it whilst ordering the wall posts by 'time_posted'
My current query does that without grouping the comments. It is:
SELECT wall.*, user_wall.*, users.username, users.avatar_id
FROM `wall`
INNER JOIN user_wall ON user_wall.wall_id = wall.wall_id
INNER JOIN users ON users.user_id = wall.user_id
WHERE user_wall.user_id=15
I hope you can understand this.
Edit:
The table 'user_wall' is a table that stores what values are on the users wall, and the 'wall' table stores what is actually posted. The user_id in the 'wall' table is a reference to who posted that post.
The current query as stated above is fully functional and returns data as such:
wall_id | user_id | wall_content | time_posted | is_reply | user_id | wall_id | username | avatar_id
1 | 1 | *content* | *time* | 0 | 2 | 1 | User1 | 1
2 | 1 | *content2* | *time2* | 0 | 2 | 2 | User1 | 1
3 | 1 | *content3* | *time3* | 1 | 1 | 3 | User1 | 1
Whereas my question is, how do you structure the query so the result is like so:
wall_id | user_id | wall_content | time_posted | is_reply | user_id | wall_id | username | avatar_id
1 | 1 | *content* | *time* | 0 | 2 | 1 | User1 | 1
3 | 1 | *content3* | *time3* | 1 | 1 | 3 | User1 | 1
2 | 1 | *content2* | *time2* | 0 | 2 | 2 | User1 | 1
Where the row with 'wall_id' 3 which has and 'is_reply' of 1 to be beneath the row with 'wall_id'. Similarly a row with an 'is_reply' of 2 will be under the row with the row with a 'wall_id' of 2.

Answer 1

Now that you've edited it I understand what you mean. This should do it:
ORDER BY IF(wall.is_reply, wall.is_reply, wall.wall_id), wall.wall_id
Format: IF(EXPRESSION, IF_TRUE, IF_FALSE)

Answer 2

SQL can't return multiple rows from one table (e.g. the wall_comments) and only one from the ones it is joined with. In other words, that can't be done. There is an alternative that will get the same results but use two SQL queries and some PHP code.
Query #1:
SELECT wall_comments.*
FROM `wall_comments`
INNER JOIN user_wall ON wall_comments.wall_id = user_wall.wall_id
WHERE user_wall.user_id=15
Query #2:
SELECT wall.*, user_wall.*, users.username, users.avatar_id
FROM `wall`
INNER JOIN user_wall ON user_wall.wall_id = wall.wall_id
INNER JOIN users ON users.user_id = wall.user_id
WHERE user_wall.user_id=15
PHP:
<?php
$result1 = mysql_query($query1);
$result2 = mysql_query($query2);
$comments = array();
while($row = mysql_fetch_assoc($result1))
{
$comments[$row['wall_id']][] = $row;
}
$walls = array();
while($row = mysql_fetch_assoc($result2))
{
$walls[] = array_merge(
$row,
array(
'comments' => isset($comments[$row['wall_id']]) ? $comments[$row['wall_id']] : array(),
),
);
}
?>