title: sqlalchemy error inserting with bind parameter missing, but works in Workbench
body: <p>I keep having a strange issue with my program doing SQL inserts. I'm periodically (once a day) sending a lot of data using pymysql in a single INSERT statement and every few days I get the following error:</p>
  
  <p><code>(sqlalchemy.exc.InvalidRequestError) A value is required for bind parameter 'D' [SQL:</code></p>
  
  <p>In my code, this is how the db is connected to and insert is done:</p>
  
  <p>Session creation:</p>
  
  <pre><code>engine = sqlalchemy.create_engine(db_host, echo = False)
  self.metadata = sqlalchemy.MetaData(engine)
  DB_session = sqlalchemy.orm.sessionmaker(bind = engine)
  session = DB_session()
  </code></pre>
  
  <p>Insert function:</p>
  
  <pre><code>def insert(self,sql):
      complete = False
      try:
          self.session.execute(sql)
          self.session.commit()
          complete = True
      except Exception as e:
          # Do some logging
      finally:
          return complete
  </code></pre>
  
  <p>And here's what a typical insert statement would look like:</p>
  
  <pre><code>INSERT INTO my_db.my_table (field_1, field_2, field_3, ... field_32) 
  VALUES(data_set1),(data_set2),(data_set3)...(data_set500) 
  ON DUPLICATE KEY UPDATE 
  field_1=VALUES(field_1), field_2=VALUES(field_2), field_3=VALUES(field_3) ... field_32=VALUES(field_32)
  </code></pre>
  
  <p>I've looked up this issue and normally it seems to happen when the user explicitly sets bind parameters and one is missing, but I don't understand why it's happening with my code where I don't set any, and I have no field name 'D' or know what that 'D' is even referring to. Also, to make things more confusing, when I plug in the EXACT same statement into MySQL Workbench, it executes with no problems.</p>
  
  <p>I'm thinking the issue might stem from trying to send too much data at the same time, because I am trying to update/insert a lot of data with a lot of fields each. But if that's the case, how much is too much data since I don't want to be splitting this into 500+ individual inserts?</p>