mysql数据去重

假设有一张书目信息表books，有时会出现同一书目信息插入两次及以上的情况。如何找出这些重复的书目信息，并删除冗余的信息？

查找出同一书目出现两次及以上的记录

select book_name,count(book_name) from books group by book_name having count(book_name)>1;

从这些重复的记录中删除冗余记录，只保留book_id最小的记录

select * from books where book_name in

(

select book_name from books group by book_name having count(book_name)>1

)

and book_id not in

(

select min(book_id) from books group by book_name having count(book_name)>1

);