text: Query 2: INSERT INTO bookshelves(name) SELECT DISTINCT bookshelf FROM books;
  
  /* This query will use a simple subquery to retrieve unique bookshelf values 
  from the books table and insert each one into the bookshelves table in the name 
  column. This is a great pattern for copying lots of data between tables.
  Confirm the success of this command by typing SELECT COUNT(*) FROM bookshelves; 
  in your SQL shell. The number should be greater than zero. */