title: Wordpress Database Query - Get latest Value from a Row depending on two other Columns
body: <p>If  "$Post_id" = "post_parent" and "user_ID" = "post_author" then i need to get "guid" as Variable. But how?</p>
  
  <p>I already have those variables:
  $post_id (is the same value of "post_parent")
  $user_id (is the same value of "post_author")</p>
  
  <p>In the Table (i think it called table right?) "posts" i have three Columns "post_parent", "post_author" and "guid".</p>
  
  <p>But i really don´t know who to do that. I already check this, but don´t know how to work with it: <a href="http://codex.wordpress.org/Function_Reference/wpdb_Class" rel="nofollow">http://codex.wordpress.org/Function_Reference/wpdb_Class</a></p>