title: MySQL Left Join bigger than the "left" table alone?
body: <p>Am I understanding what Left Join is supposed to do?</p>
  
  <p>I have a query. Call it Query A.  It returns 19 records.</p>
  
  <p>I have another query, Query B. It returns 1,400 records.</p>
  
  <p>I insert Query B into Query A as a left join, so Query A becomes:</p>
  
  <pre><code>SELECT *
  FROM tableA
  LEFT JOIN (&lt;&lt;entire SQL of Query B&gt;&gt;) ON tableA.id = tableB.id
  </code></pre>
  
  <p>Now, a Left Join means everything from Table A, and only records from Table B where they match.  So no matter what, this mixed query should not return more than the 19 records that the original Query A returns.  What I actually get is 1,000 records.</p>
  
  <p>Am I fundamentally misunderstanding how LEFT JOIN works?</p>