join 2 tables and display menu with only group name - php

Question

I have 2 tables:
group
--id
--name
category
--id
--name
--group_id
and the query:
SELECT group.id AS gid, group.name AS gname,
category.id AS cid, category.name AS cname
FROM group join category
on group.id = category.group_id
and result for it is demonstrated as below:
gid--gname--cid--cname
1 ---abc----1----def
1 ---abc----2----ggg
2 ---ccc----3----eee
2 ---ccc----4----fff
I want to show a menu like this:
abc
--def
--ggg
ccc
--eee
--fff
I can't show menu as above if I use that query (infact, I can but it's hard).
What query or a way can help me do this? Thanks so much!

Answer 1

It's a matter of presentation, but you may find it handy to use GROUP_CONCAT() in situation like this to pack categories per group
SELECT g.id gid, g.name gname, GROUP_CONCAT(CONCAT(c.id, '|', c.name) ORDER BY c.id) categories
FROM `group` g JOIN category c
ON g.id = c.group_id
GROUP BY g.id, g.name
Here is SQLFiddle demo
and then easily explode() categories column in php while you iterate over the resultset
Just to give you an idea how php part might look like using PDO
$db = new PDO('mysql:host=localhost;dbname=dbname', 'user', 'password');
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$sql = "SELECT g.id gid, g.name gname, GROUP_CONCAT(CONCAT(c.id, '|', c.name) ORDER BY c.id) categories
FROM `group` g JOIN category c
ON g.id = c.group_id
GROUP BY g.id, g.name";
$query = $db->prepare($sql);
$query->execute();
$rows = $query->fetchall(PDO::FETCH_ASSOC);
$query = null;
$db = null;
echo '<ul>';
foreach($rows as $row) {
echo '<li>' . $row['gid'] . '-' . $row['gname'];
$categories = explode(',', $row['categories']);
echo '<ul>';
foreach($categories as $category) {
list($cid, $cname) = explode('|', $category);
echo '<li>' . $cid . '-' .$cname . '</li>';
}
echo '</ul></li>';
}
echo '</ul>';
Output:
1-abc1-def2-ggg2-ccc3-eee4-fff

Answer 2

basically you have to loop for each group and printing all category belong to that group.
in php u can do this:
while( $group = mysql_fetch_array( mysql_query("SELECT id, name FROM group") ) ){
echo $group[1];
while( $category = mysql_fetch_array( mysql_query("SELECT id, name from category where group_id =" . $group[0] ) ) ){
echo $category[1];
}
}

Answer 3

Try this:
$arr = array(
array('gid'=>1, 'gname'=>'abc', 'cid'=>1, 'cname'=>'def'),
array('gid'=>1, 'gname'=>'abc', 'cid'=>2, 'cname'=>'ggg'),
array('gid'=>2, 'gname'=>'ccc', 'cid'=>3, 'cname'=>'eee'),
array('gid'=>2, 'gname'=>'ccc', 'cid'=>4, 'cname'=>'fff'),
);
$res = array();
foreach($arr as $ar){
if(empty($res[$ar['gid']])){
$res[$ar['gid']] = array(
'gid'=>$ar['gid'],
'gname'=>$ar['gname'],
);
}
$res[$ar['gid']]['category'][] = array('cid'=>$ar['cid'],'cname'=>$ar['cname']);
}
print_r($res);