title: What does Using join buffer (Block Nested Loop) mean with EXPLAIN mysql command in the Extra column?
body: <p>I am trying to optimize my query.</p>
  <p>And getting <strong>Using join buffer (Block Nested Loop)</strong>
  for one of the table with</p>
  <p><code>EXPLAIN SELECT</code> command.</p>
  <p>I have no idea what does it mean.
  I tried googling about, but I haven't found the explanation.</p>