input: Write a function to query data from MySQL, MongoDB, and PostgreSQL databases, and display the results on a web page using Python libraries for each database. The function should connect to each database, execute a predefined query, fetch the results, and then close all connections. Finally, it should render the results on the web page using a template. If the input is not applicable, return None.
  assert query_data() == None
  assert query_data() == "Data displayed on web page"
output: def query_data():
      return None