input: Write a function to connect to MySQL, MongoDB, and PostgreSQL databases, execute queries on each database, and render the results on a web page using Python libraries for all three databases. If the query is successful, return the fetched data; otherwise, return an empty list.
  assert render_page('user1')=={'data_mysql': [], 'data_mongodb': [{'name': 'John Doe'}], 'data_postgresql': []}
output: def render_page(user):
      import mysql.connector
      from pymongo import MongoClient
      import psycopg2
      
      data_mysql = []
      data_mongodb = []
      data_postgresql = []
      
      try:
          # MySQL connection and query
          mysql_conn = mysql.connector.connect(user='root', password='password', host='127.0.0.1', database='testdb')
          mysql_cursor = mysql_conn.cursor(dictionary=True)
          mysql_cursor.execute("SELECT * FROM users WHERE username = %s", (user,))
          data_mysql = mysql_cursor.fetchall()
          mysql_cursor.close()
          mysql_conn.close()
      except:
          pass
      
      try:
          # MongoDB connection and query
          mongo_client = MongoClient('mongodb://localhost:27017/')
          mongo_db = mongo_client['testdb']
          mongo_collection = mongo_db['users']
          data_mongodb = list(mongo_collection.find({'username': user}))
          mongo_client.close()
      except:
          pass
      
      try:
          # PostgreSQL connection and query
          postgresql_conn = psycopg2.connect(user='postgres', password='password', host='127.0.0.1', database='testdb')
          postgresql_cursor = postgresql_conn.cursor(cursor_factory=psycopg2.extras.RealDictCursor)
          postgresql_cursor.execute("SELECT * FROM users WHERE username = %s", (user,))
          data_postgresql = postgresql_cursor.fetchall()
          postgresql_cursor.close()
          postgresql_conn.close()
      except:
          pass
      
      return {'data_mysql': data_mysql, 'data_mongodb': data_mongodb, 'data_postgresql': data_postgresql}