title: mysql insert if value not exist in another table
body: <p>I have two tables that store value as <code>VARCHAR</code>.<br>
  I'm populating table and I want just insert values in one of tables if they are not exist in other table.<br>
  Something like:  </p>
  
  <pre><code>INSERT IF IS EMPTY(SELECT * FROM t1 where v='test') INTO t2 (v) VALUES ('test')
  </code></pre>
  
  <p>How Can I do that?  </p>