title: Is there inner join and outer join performance difference
body: <p>I read some existing codes and found out all SQLs wrote as outer join even it is inner join.
  Then, I start to think about the performance difference between if the result are same.
  In my mind, inner join should be faster than outer join.  But, I can't find any document to prove this.
  Could you help me on this?
  Thanks</p>