title: how to exclude a special condition when using group by and count()
body: <p>In a transaction table, has order_ID(PK), transaction_date, cus_ID, store_ID.
  Now I need to get all the cus_ID with when group by cus_ID, count(store_ID) = 1. There is one exception though - When cus_ID has only orders with store_ID='999'. 
  Transaction date should be during the past 365 days. 
  I have code as below:</p>
  
  <pre><code>Select cus_ID, count(store_ID) as store_count
  From trn_header
  where transanction_date From '7/30/2017' - 365 To '7/30/2017'
  group by cus_ID having store_count = 1
  </code></pre>
  
  <p>I just don't know how to exclude the '999' condition...
  thanks</p>