C#

var distinctBooks = query
                                                 .GroupBy(x => x.BookID)
                                                 .Select(x => x.FirstOrDefault());

List<FillGrid> query = (from b in db.Books
                                                                            join ba in db.BookAuthors on b.ID equals ba.BookID
                                                                            join a in db.Authors on ba.AuthorID equals a.ID
                                                                            join bn in db.BookNumbers on b.ID equals bn.BookID
                                                                            where a.AuthorFirst == splitstring[1].ToString() && a.AuthorLast == splitstring[0].ToString()
                                                                            select new FillGrid
                                                                            {
                                                                                AuthorID = a.ID,
                                                                                Author = string.Format("{0} {1}", a.AuthorFirst, a.AuthorLast),
                                                                                Title = b.Title,
                                                                                Price = (decimal)b.Price,
                                                                                BookNumber = bn.SurrogateNumber,
                                                                                BookID = b.ID,
                                                                                Count = db.BookNumbers.Count(c => c.BookID == b.ID)
                                                                            }).ToList();