title: How is it valid to use 'table.column=t.column' (when t is short for table)
body: <p>The code at the bottom works, which confuses me. I don't understand the expression:</p>
  
  <pre><code>where wands_property.age = p.age
  </code></pre>
  
  <p>because <code>p</code> is short hand for <code>wands_property</code>, so that expression seems to look like:</p>
  
  <pre><code>wands_property.age = wands_property.age
  </code></pre>
  
  <p>which is a tautology.</p>
  
  <p>How is a table, <code>wands_property</code> different when it has been given an alias <code>p</code>?</p>
  
  <p>CODE:</p>
  
  <pre><code>select w.id, p.age, w.coins_needed, w.power 
  from wands w join wands_property p on w.code = p.code 
  where p.is_evil = 0
  and w.coins_needed = (
      select min(wands.coins_needed)
      from wands 
      join wands_property on wands.code = wands_property.code 
      where wands_property.age = p.age
      and wands.power = w.power)
  order by power desc, age desc
  </code></pre>