upd. цена со скидкой SOLD OUT

CREATE TABLE Books{
idBook int NOT NULL,
BookName nvarchar (200) NOT NULL,
ISBN nvarchar(20) NULL
Cost decimal NULL, // цена в рублях 
BookSold int NOT NULL); //количество проданных книг
};

CREATE TABLE Authors{
idAuthor int NOT NULL,
AuthorName nvarchar(300) NOT NULL,
Country nvarchar(300))
};

CREATE TABLE Books_ Authors{
idBookAuthor int NOT NULL,
idBook int NOT NULL,
idAuthor Int NOT NULL)
};