input: Write a function to query and display data from three different databases (MySQL, MongoDB, and PostgreSQL) on a web page using their respective Python libraries. The function should connect to each database, execute the specified query, fetch the results, close the connections, and then render the results on a webpage. The function should return a rendered webpage with the data from all three databases.
  assert render_page(None)=='template.html', {'data_mysql': result_mysql, 'data_mongodb': result_mongodb, 'data_postgresql': result_postgresql}
  assert render_page(None)=='template.html', {'data_mysql': [], 'data_mongodb': [], 'data_postgresql': []}
  assert render_page(None)=='template.html', {'data_mysql': None, 'data_mongodb': None, 'data_postgresql': None}
output: def render_page(template_name):
      import mysql.connector
      from pymongo import MongoClient
      import psycopg2
      from jinja2 import Template
  
      # MySQL connection and query
      mysql_conn = mysql.connector.connect(host='localhost', user='user', password='password', database='dbname')
      mysql_cursor = mysql_conn.cursor()
      mysql_cursor.execute("SELECT * FROM table_name")
      result_mysql = mysql_cursor.fetchall()
      mysql_cursor.close()
      mysql_conn.close()
  
      # MongoDB connection and query
      mongo_client = MongoClient('localhost', 27017)
      mongo_db = mongo_client['dbname']
      mongo_collection = mongo_db['collection_name']
      result_mongodb = list(mongo_collection.find())
      mongo_client.close()
  
      # PostgreSQL connection and query
      postgresql_conn = psycopg2.connect(host='localhost', dbname='dbname', user='user', password='password')
      postgresql_cursor = postgresql_conn.cursor()
      postgresql_cursor.execute("SELECT * FROM table_name")
      result_postgresql = postgresql_cursor.fetchall()
      postgresql_cursor.close()
      postgresql_conn.close()
  
      # Render the results on a webpage
      with open(template_name, 'r') as file:
          template = Template(file.read())
      rendered_page = template.render(data_mysql=result_mysql, data_mongodb=result_mongodb, data_postgresql=result_postgresql)
  
      return rendered_page