input: Write a python function to connect to a SQLite database and execute a SELECT query.
  assert execute_query("SELECT name FROM sqlite_master WHERE type='table';") == [('users',)]
  assert execute_query("SELECT * FROM users WHERE id = 1;") == [(1, 'JohnDoe', 'john@example.com', 'hashed_password')]
  assert execute_query("SELECT * FROM users WHERE username = 'Alice';") == [(2, 'Alice', 'alice@example.com', 'hashed_password')]
output: def execute_query(query):
      import sqlite3
      
      # Establish a connection to the SQLite database
      conn = sqlite3.connect('example.db')
      cursor = conn.cursor()
      
      # Execute the provided query
      cursor.execute(query)
      
      # Fetch all results from the executed query
      results = cursor.fetchall()
      
      # Close the cursor and the connection
      cursor.close()
      conn.close()
      
      return results