title: Another SQL-Interrogation
body: <p>I've got another problem on my SQL Tables but this time I've got more tables linked together.
  What I realised and where I'm stuck:</p>
  
  <p>I have tables about jobs, wages, employees.</p>
  
  <p>I've done a query with these conditions:</p>
  
  <p>The employee with the biggest wage in my company:</p>
  
  <pre><code>select employee_id, count(employee) as  wage 
  from number_statistics 
  group by employee_id 
  having count(employee_id) in 
  (select max(count(employee_id)) from number_statistics group by employee_id);
  </code></pre>
  
  <p>This will show the ID of my employee with the biggest wage.</p>
  
  <p>Where I'm stuck:</p>
  
  <p>My next task is to create this query:</p>
  
  <p>I need to display the employee with the biggest wage on three age categories:
  Between 21-30; 30-45; 45-60;</p>
  
  <p>The problem is that I don't have a field name AGE (and I'm not allowed to use one) in my tables.
  I only have the birth date of my employees.</p>