title: MySql query for crosstable select
body: <p>packages:
  package_id, user_id</p>
  
  <p>transactions:
  product_id,user_id,package_id</p>
  
  <p>I want to select rows in transactions that have package_id null or 0
  but only when there are other transactions with same user_id where package id is greater than 0
  is that possible. Sorry for bad English... I tried goggling it, but couldn't guess a correct question for Google query.</p>
  
  <p>I know that title is not ok, so anybody please propose a better one.</p>
  
  <p>Gwynnbleid1</p>