title: Dropping then adding a constraint fails in oracle
body: <p>I'm trying to move a primary key constraint to a different column in oracle. I tried this:</p>
  
  <pre><code>ALTER TABLE MY_TABLE
  DROP CONSTRAINT c_name;
  
  ALTER TABLE MY_TABLE
  ADD CONSTRAINT c_name PRIMARY KEY
  (
    "COLUMN_NAME"
  ) ENABLE;
  </code></pre>
  
  <p>This fails on the add constraint with an error saying the the constraint already exists even though i just dropped it. Any ideas why this is happening</p>