title: How do I force join inside a left join branch?
body: <p>I need to LEFT join to entire t2+t3 branch, but if I can find a matching join between t1 and t2, I want to enforce the t2 and t3 join.  </p>
  
  <pre><code>   SELECT T1.name,T2.bob,T3.a
       FROM T1
  LEFT JOIN T2 ON t1.id = t2.t1_id
       JOIN T3 ON t2.id = T3.t2_id
  </code></pre>
  
  <p>What is the syntax?</p>
  
  <p>Sample data:</p>
  
  <pre><code>T1 [id,name]
  1 aaa
  2 bbb
  3 ccc
  
  T2 [id,t1_id,bob]
  1,1,777
  2,1,888
  2,2,999
  
  T3[id,t2_id,a]
  1,2,'yeh'
  </code></pre>
  
  <p>EXPECTED RESULT:</p>
  
  <pre><code> [name] , [a]   , [bob]
    aaa   , 'yeh' , 888
    bbb   , NULL  , NULL
    ccc   , NULL  , NULL
  </code></pre>