title: SQL interview question
body: <p>I got following question on an interview:
  Given a table of natural numbers with some missing ones, provide output of two tables, beginning of number gap in first table
  and ending in second.
  Example:</p>
  
  <pre>
   ____    ________
  |    |   |   |   |
  | 1  |   | 3 | 3 |
  | 2  |   | 6 | 7 |
  | 4  |   | 10| 12|
  | 5  |   |___|___|
  | 8  |
  | 9  |
  | 13 |
  |____|
  </pre>