title: Arrange data in MySQL tables
body: <p>I have a users table and a categories table which already contain data,
  I also have a third table which called <code>user_category</code> which has three <code>columns(id,user_id,category_id)</code>.</p>
  
  <p>When the user first register he must choose a category or more than one from a dropdown. I want to insert the id of the user to <code>user_id</code> columns and the id of each category to the <code>category_id</code> so if the user choose more than one category he will have more than one record in the <code>user_category</code> table.</p>