[Zope] using a ZMySQL database connection object in an external method

[Luby Liao]

Is there a How-To, or are there some code fragments that will help me
use a ZMySQL (or a psycopg) database connection object in an external
method?  Given that mysql_connection is a ZMySQL database connection
object, I expected

  mysql_connection.db.select_db('database') 

to work. But I got 

  Error Type: ProgrammingError
  Error Value: (2014, "Commands out of sync; You can't run this command now")

Any help is appreciated.  cheers, Luby