book表中的数据：

根据所有字段去重：

SELECT DISTINCT * from dbo.book 

sql根据多个字段去重：

SELECT title,isbn,author_id ,page_count  from dbo.book 
group by title,isbn,author_id ,page_count
 

或者：
SELECT DISTINCT title,isbn,author_id ,page_count from dbo.book

sql根据多个字段去重,并且返回所有字段：

SELECT * from dbo.book a where id in (SELECT max(id) from dbo.book 
group by title,isbn,author_id ,page_count )

如果数据量比较大的话in会有效率问题，可以采用以下写法

SELECT a.* from dbo.book a , (SELECT max(id) as id from dbo.book 
group by title,isbn,author_id ,page_count )b where a.id = b.id

有问题欢迎指正