title: Insert into database and check if row already exist
body: <p>I have simple input and I need help with MySQL.</p>
  
  <p>When you click the submit button, PHP will need to check if the row already exist and only insert a new one if not.</p>
  
  <p>I know the <code>INSERT</code> part, but don't know how to check if the row already exists.</p>