title: MySQL Column definition for hasMany relationship in Yii2
body: <p>I have an employees table defined with their alphanumeric employee_id (currently 9-characters but can increase upto 15) as the key:</p>
  
  <pre><code>CREATE TABLE employee (
      emp_id VARCHAR(15) NOT NULL PRIMARY KEY,
      emp_name VARCHAR(255) NOT NULL,
      ...
  );
  </code></pre>
  
  <p>Now, I've to create a Group entity where each employee can be part of multiple groups:</p>
  
  <pre><code>CREATE TABLE group (
      group_id VARCHAR(15) NOT NULL PRIMARY KEY,
      group_name VARCHAR(255) NOT NULL,
      employees ????, &lt;--- how should this be defined?
      FOREIGN KEY fk_emp(employees) REFERENCES employee(emp_id)
  );
  </code></pre>
  
  <p>I can create the controller and view for this using gii or manually, without an issue. The group creation/update form will have a multi-select for employees.</p>
  
  <p>As an alternative, does Yii2 support sets?</p>