title: psycopg2.OperationalError: FATAL: role "postgresql" does not exist
body: <p>I am a postresql novice.
  When I was ready to migrate INSTALLED_APPS in 'settings' to database,there appeared the following error:</p>
  
  <pre><code>psycopg2.OperationalError: FATAL:  role "postgresql" does not exist
  </code></pre>
  
  <p>and I have displayed the full exception message:</p>
  
  <pre><code>c:\fanhuaxiu\Scripts&gt;activate
  (fanhuaxiu) c:\fanhuaxiu\Scripts&gt;cd ..
  
  (fanhuaxiu) c:\fanhuaxiu&gt;cd fhx
  
  (fanhuaxiu) c:\fanhuaxiu\fhx&gt;python manage.py migrate
  Traceback (most recent call last):
    File "C:\fanhuaxiu\lib\site-packages\django\db\backends\base\base.py", line 216, in ensure_connection
      self.connect()
    File "C:\fanhuaxiu\lib\site-packages\django\db\backends\base\base.py", line 194, in connect
      self.connection = self.get_new_connection(conn_params)
    File "C:\fanhuaxiu\lib\site-packages\django\db\backends\postgresql\base.py", line 168, in get_new_connection
      connection = Database.connect(**conn_params)
  
    File "C:\fanhuaxiu\lib\site-packages\psycopg2\__init__.py", line 130, in connect
      conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
  psycopg2.OperationalError: FATAL:  role "postgresql" does not exist
  </code></pre>
  
  <p>It has taken me nearly 2 hours to find a solution and failed 233333.
  Thanks in advance.</p>