title: mysql select distinct where clause
body: <p>I have this table, and I want to select all distinct  user_id values where there is both an event='AAAAAAAAAA' and event ='XXXXXXXXXX' (i.e. only result should be user_id=123456789)</p>
  
  <pre><code>unique_row_id  user_id          event       event_timestamp
  ----------------------------------------------------------------
  0              123456789        AAAAAAAAAA  2010-01-20 15:00:00
  1              123456789        abcdefghij  2010-01-20 15:00:05
  2              123456789        XXXXXXXXXX  2010-01-20 15:00:15
  3              987654321        AAAAAAAAAA  2010-01-20 16:00:00
  4              987654321        abcdefghij  2010-01-20 16:00:05
  5              987654321        abcdefghij  2010-01-20 16:00:15
  6              111111111        XXXXXXXXXX  2010-01-20 16:01:00
  7              111111111        XXXXXXXXXX  2010-01-20 16:01:05
  8              111111111        XXXXXXXXXX  2010-01-20 16:01:15
  </code></pre>
  
  <p>I've tried both:</p>
  
  <pre><code>SELECT distinct user_id from mydata where event='AAAAAAAAAA' and event='XXXXXXXXXX'
  </code></pre>
  
  <p>which gives me an empty result set, and </p>
  
  <pre><code>SELECT distinct user_id from mydata where event='AAAAAAAAAA' or event='XXXXXXXXXX'
  </code></pre>
  
  <p>which gives me everything.  Any suggestions - I'm guessing I need to go down the 'join' road here do I?</p>