title: creating an index for a join statement
body: <p>I have a LEFT JOIN select statement that retrieves values from 2 tables: tableA and tableB. The syntax is as follows:</p>
  
  <pre><code>SELECT tableA.first, tableA.middle, tableA.last, tableB.full FROM tableA LEFT JOIN     
  tableB ON tableB.full LIKE concat('%',tableA.middle,'%');
  </code></pre>
  
  <p>What is the best type of index to have for this statment? I've tried one on tableB.full but according to my EXPLAIN statement, it is not being used.</p>
  
  <p>Note: though it's probably obvious, I am a newbie to join statements. 
  thx.</p>