title: Error while connecting postgres db from airflow
body: <p>Using:</p>
  
  <p><code>sql_alchemy_conn = db+postgresql://username:xxx@127.0.0.1:5432/airflow</code>
  gives error:</p>
  
  <blockquote>
    <p>sqlalchemy.exc.NoSuchModuleError: Can't load plugin: sqlalchemy.dialects:db.postgresql</p>
  </blockquote>
  
  <p>and when using:</p>
  
  <p><code>sql_alchemy_conn = postgresql+psycopg2://username:xxx@localhost:5432/airflow</code>
  I could run the <code>airlfow webserver -p 8080</code> but while running the scheduler: <code>airflow scheduler</code> it throws error:</p>
  
  <blockquote>
    <p>ModuleNotFoundError: No module named 'MySQLdb'
    <a href="https://i.stack.imgur.com/1SZlW.png" rel="noreferrer"><img src="https://i.stack.imgur.com/1SZlW.png" alt="enter image description here"></a></p>
  </blockquote>
  
  <p>packages versions I am using:</p>
  
  <pre><code>psycopg2==2.7.3.1
  sqlalchemy==1.1.15
  sqlalchemy-redshift== 0.7.0
  apache_airflow=1.8.2
  </code></pre>
  
  <p>Earlier <code>sql_alchemy_conn = db+postgresql://username:xxx@127.0.0.1:5432/airflow</code> did worked for me - 2 months ago. I don't know what is the problem now.</p>