title: How to make a difficult GROUP query for getting information by 2 groups
body: <p>There is the following table: </p>
  
  <pre><code>Product(maker, model, type)
  </code></pre>
  
  <p>Maker - maker of device, type is PC, Laptop, Printer, model is primary key. I need to get all makers which makes devices with the same type only and makes more than 1 model. Information for showing is maker, type. I've got the following query: </p>
  
  <pre><code>SELECT maker, type, count(*) as how_many 
  FROM Product 
  GROUP BY maker, type 
  HAVING count(*) &gt; 1
  </code></pre>
  
  <p>But I don't know how to get makers with the same type of devices.  </p>
  
  <p>UPDATE: for, example, there are the following records:</p>
  
  <pre><code>A - 01 - Printer
  A - 02 - PC
  A - 03 - Laptop
  B - 04 - Printer
  B - 05 - Printer
  </code></pre>
  
  <p>B is good maker, because all his devices has got the same type - 'Printer'. Have I fixed you?</p>