input: Write a python function to execute an SQL query to select all columns from a table.
  assert execute_query('SELECT * FROM users') == expected_result_for_users
  assert execute_query('SELECT * FROM products') == expected_result_for_products
  assert execute_query('SELECT * FROM orders') == expected_result_for_orders
output: import sqlite3
  
  def execute_query(query):
      connection = sqlite3.connect('example.db')
      cursor = connection.cursor()
      cursor.execute(query)
      result = cursor.fetchall()
      connection.close()
      return result