title: SQL: keep one record from n-records with same foreign key
body: <p>I have some records and want only to keep the lowest (min) number from a customer:</p>
  
  <p>This:</p>
  
  <pre><code>Customer | Number
  1        | 2
  1        | 4
  2        | 1
  1        | 3
  2        | 2
  </code></pre>
  
  <p>should be tranformed via sql to:</p>
  
  <pre><code>Customer | Number
  1        | 2
  2        | 1
  </code></pre>
  
  <p>using Sybase ADS local table.</p>