避免重复值并在mysql数据库中的相同行中获取其他数据集

I have a database table that contain several projects. I want to show each project in a tab view. so I want to get each project name once and fetch other details under that project name. My table looks like below.

+-------------+----------+--------------+---------+-------------+
| activity_id | activity | project_name | user_id | description |
+-------------+----------+--------------+---------+-------------+
|       1     |    A     | New Project  |    5    |   Project   |
|       2     |    B     | New Project  |    5    |   Project   |
|       3     |    C     | New Project  |    5    |   Project   |
|       4     |    D     | New Project  |    5    |   Project   |
|       5     |    E     | New Project  |    5    |   Project   |
|       6     |    A     | Old Project  |    5    |   New one   |
|       7     |    B     | Old Project  |    5    |   New one   |
|       8     |    C     | Old Project  |    5    |   New one   |
|       9     |    A     | Another One  |    5    |   Test 01   |
|      10     |    B     | Another One  |    5    |   Test 01   |
|      11     |    C     | Another One  |    5    |   Test 01   |
|      13     |    D     | Another One  |    5    |   Test 01   |
+-------------+----------+--------------+---------+-------------+

Is there a way to get this table like below array?

['New Project'] =>
      [0] =>
          ['activity_Id']   =>   '1'
          ['activity']      =>   'A'
          ['user_id']       =>   '5'
          ['description']   =>   'project'
      [1] =>
          ['activity_Id']   =>   '2'
          ['activity']      =>   'B'
          ['user_id']       =>   '5'
          ['description']   =>   'Project'

and like vice..?

This would do the trick:

$stm = $pdo->query('SELECT * FROM tablename');
while( $row = $stm->fetch(PDO::FETCH_ASSOC) )
{
    $info = array(
        'activity_id' => $row['activity_id'],
        'activity' => $row['activity'],
        'user_id' => $row['user_id'],
        'description' => $row['description']
    );
    if( array_key_exists($row['project_name'], $array) && is_array($array[$row['project_name']]) )
    {
        $array[$row['project_name']][] = $info;
    }
    else
    {
        $array[$row['project_name']] = array();
        $array[$row['project_name']][] = $info;
    }
}

two queries will do it easily, first query to fetch distinct project name and from second query data according to first query project name.

query select distinct project_name from table for loop on this result query select activity_Id, activity, user_id, description from table where project_name = result from first query for loop on this result make array as you wish

No, AFAIK, you can't get this kind of nesting directly with active record -now in CI3 known as Query Builder- (but you probably could achieve it with ORM, frameworks like CakePHP and Laravel have their own implementations).

The only way is to create a new array and iterate over the result array you got from the model in order to build the structure you need.

You can check CI3 docs about Query Builder here: http://www.codeigniter.com/userguide3/database/query_builder.html