title: MySql - Multitable - AND is not the correct choice, but what is?
body: <p>I have two tables:</p>
  
  <p>mytable1</p>
  
  <pre><code>UserId (int) (primary_key)
  Save (blob)
  </code></pre>
  
  <p>mytable2</p>
  
  <pre><code>UserId (int) (primary_key)
  Save (blob)
  </code></pre>
  
  <p>I make the following mysql command:</p>
  
  <pre><code> UPDATE mytable1 tb1, mytable2 tb2 SET tb1.Save='', tb2 .Save='' WHERE tb1.UserId=25 AND dbSv1.UserId=25
  </code></pre>
  
  <p>When both tables have a user with UserId = 25, then this works and Save is set to ''. However, if one table does not have a user with UserId = 25, but the other one does, then Save is not set to '' in the one that does. This is not the behaviour I want.</p>
  
  <p>OR is not the thing to use, as other Saves will be set to '' which do not have an UserId of 25. So what do I need?</p>