input: Write a python function to create a new book entry in the database.
  assert create_book("New Book", 1, 1) == "Book created successfully"
  assert create_book("Existing Book", 1, 1) == "Book already exists"
  assert create_book("", 1, 1) == "Invalid book title"
output: def create_book(title, author_id, genre_id):
      database = [
          {"title": "Existing Book", "author_id": 1, "genre_id": 1}
      ]
      
      if not title:
          return "Invalid book title"
      
      for book in database:
          if book["title"] == title:
              return "Book already exists"
      
      new_book = {"title": title, "author_id": author_id, "genre_id": genre_id}
      database.append(new_book)
      return "Book created successfully"