title: Bulk update in SQLAlchemy Core using WHERE
body: <p>I have managed to work with the bulk insert in SQLAlchemy like:</p>
  
  <pre><code>conn.execute(addresses.insert(), [ 
     {'user_id': 1, 'email_address' : 'jack@yahoo.com'},
     {'user_id': 1, 'email_address' : 'jack@msn.com'},
     {'user_id': 2, 'email_address' : 'www@www.org'},
     {'user_id': 2, 'email_address' : 'wendy@aol.com'},
  ])
  </code></pre>
  
  <p>What I need now is something equivalent for update. I have tried this:</p>
  
  <pre><code>conn.execute(addresses.insert(), [ 
     {'user_id': 1, 'email_address' : 'jack@yahoo.com', 'id':12},
     {'user_id': 1, 'email_address' : 'jack@msn.com', 'id':13},
     {'user_id': 2, 'email_address' : 'www@www.org', 'id':14},
     {'user_id': 2, 'email_address' : 'wendy@aol.com', 'id':15},
  ])
  </code></pre>
  
  <p>expecting that each row gets updated according to the 'id' field, but it doesn't work. I assume that it is because I have not specified a WHERE clause, but I don't know how to specify a WHERE clause using data that is included in the dictionary.</p>
  
  <p>Can somebody help me?</p>