input: Write a function that connects to three different databases: MySQL, MongoDB, and PostgreSQL, and queries the data from each database. The function should then display the queried data on a web page. The function should use the respective libraries for each database. The returned webpage should include the queried data from all three databases.
  
  def connect_and_query_databases():
      import pymysql
      from pymongo import MongoClient
      import psycopg2
  
      # connect to MySQL
      connection_mysql = pymysql.connect(host='localhost', user='root', password='password', database='db_name')
  
      # connect to MongoDB
      client = MongoClient('mongodb://localhost:27017')
  
      # connect to PostgreSQL
      connection_postgresql = psycopg2.connect(host='localhost', user='postgres', password='password', dbname='db_name')
  
      # define a query for each database
      query_mysql = 'SELECT * FROM table_name'
      query_mongodb = {'name': 'John Doe'}
      query_postgresql =  'SELECT * FROM table_name WHERE age > 18'
  
      # execute the query and fetch the results
      result_mysql = connection_mysql.execute(query_mysql)
      result_mongodb = client.db_name.collection_name.find(query_mongodb)
      result_postgresql = connection_postgresql.execute(query_postgresql)
  
      # close the connections
      connection_mysql.close()
      client.close() 
      connection_postgresql.close()
  
      # render the results on webpage
      def render_page(request):
          return render(request, 'template.html', {
              'data_mysql': result_mysql, 
              'data_mongodb': result_mongodb,
              'data_postgresql': result_postgresql
          })
  
  assert connect_and_query_databases().render_page('example_request') is not None
output: def connect_and_query_databases():
      import pymysql
      from pymongo import MongoClient
      import psycopg2
  
      # connect to MySQL
      connection_mysql = pymysql.connect(host='localhost', user='root', password='password', database='db_name')
      cursor_mysql = connection_mysql.cursor()
  
      # connect to MongoDB
      client = MongoClient('mongodb://localhost:27017')
      db_mongodb = client.db_name
      collection_mongodb = db_mongodb.collection_name
  
      # connect to PostgreSQL
      connection_postgresql = psycopg2.connect(host='localhost', user='postgres', password='password', dbname='db_name')
      cursor_postgresql = connection_postgresql.cursor()
  
      # define a query for each database
      query_mysql = 'SELECT * FROM table_name'
      query_mongodb = {'name': 'John Doe'}
      query_postgresql =  'SELECT * FROM table_name WHERE age > 18'
  
      # execute the query and fetch the results
      cursor_mysql.execute(query_mysql)
      result_mysql = cursor_mysql.fetchall()
  
      result_mongodb = list(collection_mongodb.find(query_mongodb))
  
      cursor_postgresql.execute(query_postgresql)
      result_postgresql = cursor_postgresql.fetchall()
  
      # close the connections
      cursor_mysql.close()
      connection_mysql.close()
      client.close() 
      cursor_postgresql.close()
      connection_postgresql.close()
  
      # render the results on webpage
      def render_page(request):
          return render(request, 'template.html', {
              'data_mysql': result_mysql, 
              'data_mongodb': result_mongodb,
              'data_postgresql': result_postgresql
          })
  
      return render_page