title: How to perform a left join in SQLALchemy?
body: <p>I have a SQL query which perfroms a series of left joins on a few tables:</p>
  
  <pre><code>SELECT
  &lt;some attributes&gt;
  FROM table1 t1
  INNER JOIN table2 t2
        ON attr = 1 AND attr2 = 1
  LEFT JOIN table3 t3
      ON t1.Code = t2.Code AND t3.Date_ = t1.Date_
  LEFT JOIN tabl4 t4
      ON t4.Code = t1.code AND t4.Date_ = t1.Date_
  </code></pre>
  
  <p>So far, I have:</p>
  
  <pre><code>(sa.select([idc.c.Code])
              .select_from(
                  t1.join(t2, and_(t1.c.attr == 1, t2.c.attr2 = 1))
                  .join(t3, t3.c.Code == t1.c.Code)))
  </code></pre>
  
  <p>but I can't figure out how to make the join a <code>LEFT JOIN</code>.</p>