将mysql值显示为类别和项目

I have the following two tables in my mysql database.

Table Name: groups

 id    group_name
 1     Garments
 2     Computer Accessories 
 3     Food

Table Name: account

 id     group_id    account_name
 1         1        T-shirt
 2         1        Jeans
 3         2        Motherboard
 4         2        Mouse

What I am trying to display is like following:

Garments 
      T-Shirt
       Jeans
Computer Accessories
       Motherboard
       Mouse
Food

I have tried the following query but could not make the output like above

 SELECT group_name,accounts.account_name,accounts.id FROM `groups`
 LEFT JOIN accounts ON accounts.group_id=groups.id 

If I run the query it displays like following:

  Garments                T-Shirt
  Garments                Jeans
  Computer Accessories    Motherboard
  Computer Accessories    Mouse
  Food                    NULL

Could you please show me how to display the output like I have mentioned above. Just for your information I am using Codeigniter.

Thanks a lot in advance :)

Here is the query for this purpose

select
  group_name as Group_name,
  group_concat(account_name) as Accounts
from garments
  left join account
    on account.group_id = garments.id
group by garments.group_name

Use group concat. This will display this result then you can explode accounts on php end

Group_name              Accounts
Computer Accessories    Motherboard,Mouse
Food                    (NULL)
Garments                T-shirt,Jeans

$categories = mysql_query('select * from groups');
while($category = mysql_fetch_array($categories))
{
   $ID = $category['id'];
   $category_name = $category['group_name'];
   echo $category_name;

   $accounts = mysql_query("select * from account where group_id = $ID");
   while($account = mysql_fetch_array($accounts))
   {
      $account_name = $account['account_name'];
      echo 'TAB TAB TAB '.$account_name;
   }
}

You can place Cateogory_name and account_name into their container's and make output better .