title: Oracle: how to UPSERT (update or insert into a table?)
body: <p>The UPSERT operation either updates or inserts a row in a table, depending if the table already has a row that matches the data:</p>
  
  <pre><code>if table t has a row exists that has key X:
      update t set mystuff... where mykey=X
  else
      insert into t mystuff...
  </code></pre>
  
  <p>Since Oracle doesn't have a specific UPSERT statement, what's the best way to do this?</p>