How to pivot horizontally Author names, and group by Book title. One row per book with multiple authors

Question

I have 3 tables - Book, Author, BookAuthorReference
A book can have multiple authors, and when I do straight query I get multiple rows per book
SELECT <columns>
FROM Book b, Author a, BookAuthorReference ba
where ba.BookId = b.BookId and
ba.AuthorId = a.AuthorId
I want to get the results as ONE row per book, and Authors separated by commas, like:
SQL 2008 internals book    Paul Randal, Kimberly Tripp, Jonathan K, Joe Sack...something like this
Thank you in advance

Answer 1

This can by done by straying into XML land. The syntax is anything but intuitive, but it works. And moreover, it is guaranteed to work.
SELECT b.Title, substring(a.Authors, 1, len(a.Authors) - 1) AS Authors
FROM   Books b
CROSS  APPLY (SELECT a.Author + ','
              FROM   BookAuthorReference ba
              JOIN   Authors a ON a.AuthorID = ba.AuthorID
              WHERE  ba.BookID = a.BookID
              ORDER  BY ba.AuthorNo
              FOR XML PATH('')) AS a(Authors)
Erland Sommarskog, SQL Server MVP, [email protected]