Which query option is more productive?

Question

PHP

There are two tables clients_case and clients of the following structure
Clients

clients_case
+----+-------------------------------------+------------+
| id | cctitle                             |  ccclients |
+----+-------------------------------------+------------+
|  1 | Подготовка бизнес-плана             | 2, 3, 7    |
|  2 | Перевод документов                  | 4,5        |
+----+-------------------------------------+------------+

clients
+----+-------------------------------+
| id | clname                        |
+----+-------------------------------+
|  1 | Клиент 1                      |
|  2 | Клиент 2                      |
|  3 | Клиент 3                      |
|  4 | Клиент 4                      |
|  5 | Клиент 5                      |
|  6 | Клиент 6                      |
|  7 | Клиент 7                      |
+----+-------------------------------+

The site displays a list of case-s (10 per page) with a sublist of customer names.

$sql = "SELECT cc.id, cc.cctitle, cc.ccclients, GROUP_CONCAT(CONCAT(cl.id,',', CAST(cl.clname AS CHAR)) ORDER BY cl.clname SEPARATOR ';') AS cln
        FROM clients_case AS cc
        LEFT JOIN clients AS cl ON FIND_IN_SET (cl.id, cc.ccclients) > 0
        GROUP BY cc.id";
$data = $this->db->select_limit($sql, 0, $size);

whether the correct solution is chosen, or is it better to create another table

case_to_case
+----+--------------+-----------+
| id | client_id    | case_id   |
+----+--------------+-----------+
|  2 | 2            | 1         |
|  3 | 3            | 1         |
|  4 | 4            | 2         |
|  5 | 5            | 2         |
|  7 | 7            | 1         |
+----+--------------+-----------+

and make a request like this

$sql = "SELECT * FROM clients_case";
      $data = $this->db->select_limit($sql, 0, $size);
      
      $sql = "SELECT DISTINCT cc.*, cc.id AS id, cl.*
          FROM case_to_case AS cc 
          LEFT JOIN clients AS cl ON cl.id = cc.client_id
          GROUP BY cl.id";
      $data2 = $this->db->query($sql);
      
      foreach($data as $k => $v)
      {
        foreach($data2 as $k2 => $rec)
        {
          if($rec['case_id'] == $v['id'])
          {
            $data[$k]['clients'][] = $data2[$k2];
          }
        }
      }

What do you think is the better implementation option?

Answer 1

It's just that the first option is not correct, from the point of view of relational databases. In the "ccclients" column, you are supposed to store the user IDs that belong to this case. This is essentially a Many-to-Many implementation, but this option is not correct. The second option is correct, when Users, Cases, and relationships between users and cases are stored in different tables. Then there will be no problems with selecting Cases and Users.

Answer 2

another more correct one. find_in_set doesn't use keys