input: Write a function to query and display data from three different databases (MySQL, MongoDB, and PostgreSQL) on a web page using respective libraries. Ensure that the function connects to each database, executes a predefined query, fetches the results, and finally renders these results on a webpage.
  
  def query_and_display_data():
      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()
  
      return {
          'data_mysql': result_mysql, 
          'data_mongodb': result_mongodb,
          'data_postgresql': result_postgresql
      }
  
  assert query_and_display_data() == {
      'data_mysql': connection_mysql.execute('SELECT * FROM table_name'), 
      'data_mongodb': client.db_name.collection_name.find({'name': 'John Doe'}),
      'data_postgresql': connection_postgresql.execute('SELECT * FROM table_name WHERE age > 18')
  }
output: 
  def query_and_display_data():
      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_mongo = client.db_name
      collection_mongo = db_mongo.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_mongo.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()
  
      return {
          'data_mysql': result_mysql,
          'data_mongodb': result_mongodb,
          'data_postgresql': result_postgresql
      }
  