title: Left join in sql table?
body: <p>I have the following SQL Server table:</p>
  
  <pre><code>+-------+----------+----------+----------+
  | group | subgroup | position |  value   |
  +-------+----------+----------+----------+
  | D924  | A        | 50       | 9144142  |
  | D924  | A        | 52       | 9268118  |
  | D924  | A        | 60       | 9144588  |
  | D924  | A        | 70       | 10116006 |
  | D924  | A        | 110      | 9074177  |
  | D924  | A        | 171      | 7367052  |
  | D924  | A        | 180      | 10118595 |
  | D924  | A        | 190      | 9074522  |
  | D924  | B        | 150      | 12423396 |
  | D955  | ...      | ...      | ...      |
  +-------+----------+----------+----------+
  </code></pre>
  
  <p>I need to list all the <code>position</code> for every <code>subgroup</code> <strong>within the same</strong> <code>group</code></p>
  
  <p>Like so:</p>
  
  <pre><code>+-------+----------+----------+----------+
  | group | subgroup | position |  value   |
  +-------+----------+----------+----------+
  | D924  | A        | 50       | 9144142  |
  | D924  | A        | 52       | 9268118  |
  | D924  | A        | 60       | 9144588  |
  | D924  | A        | 70       | 10116006 |
  | D924  | A        | 110      | 9074177  |
  | D924  | A        | 171      | 7367052  |
  | D924  | A        | 180      | 10118595 |
  | D924  | A        | 190      | 9074522  |
  | D924  | A        | 150      |          |
  | D924  | B        | 50       |          |
  | D924  | B        | 52       |          |
  | D924  | B        | 60       |          |
  | D924  | B        | 70       |          |
  | D924  | B        | 110      |          |
  | D924  | B        | 171      |          |
  | D924  | B        | 180      |          |
  | D924  | B        | 190      |          |
  | D924  | B        | 150      | 12423396 |
  | D955  | ...      | ...      | ...      |
  +-------+----------+----------+----------+
  </code></pre>
  
  <p>I would like to achieve the result table in a single SQL query. Can you advise?</p>