title: Peformance of using Inner Join within leftjoin v.s. multiple leftjoins
body: <p>I have a question about MySQL performance</p>
  
  <p>Query1:</p>
  
  <pre><code>select departments.*, booth_feature.some_feature
  from departments
  left join booth on booth.dept_id = departments.dept_id
  left join booth_feature  on  booth.booth_id=booth_feature.booth_id
  </code></pre>
  
  <p>Query2:</p>
  
  <pre><code>select departments.*, booth_feature.some_feature
  from departments
  left join (booth, booth_feature) on ( booth.dept_id = departments.dept_id and booth.booth_id=booth_feature.booth_id)
  </code></pre>
  
  <p>Assuming: 
  department can have multiple booths</p>
  
  <p>1 booth => 1 booth feature</p>
  
  <p>both department and booth tables are big tables.</p>
  
  <p>Using explain, the first query seems to be better (it checks on booth before booth_feature), despite the fact that left join is generally more expensive than inner join. Is that right? </p>