title: SQLAlchemy integrity error : Column is not Unique
body: <p>I am loading the json data into database created by SQLAlchemy:</p>
  
  <pre><code>with open('test_data.json') as f:
  data=f.read()
  jsondata=json.loads(data)
  
  
  for row in jsondata['rows']:
      r = Review(row['business_id'])
  
  
  session.add(r)
  session.commit()
  </code></pre>
  
  <p>I am storing the business id of json file into business_id column but i always get an integrity error of this sort:</p>
  
  <pre><code>sqlalchemy.exc.IntegrityError: (IntegrityError) column business_id is not unique u'INSERT INTO    rev (business_id) VALUES (?)' (u'vcNAWiLM4dR7D2nwwJ7RPCA',)
  </code></pre>