SQL根据多个字段去重查询 返回所有字段

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

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

 

// 去重字段：  AtWork  ，EmployeeNum ；  因为我这AtWork字段 存储的是日期加时间 例如：（2020-02-02 08:02:02） ，所以用 SUBSTRING截取 年月日进行去重了；

SELECT * from [dbo].[SwipeCardData] a where id in (SELECT max(id) from [dbo].[SwipeCardData]group by SUBSTRING([AtWork], 1, 10),EmployeeNum)  and SUBSTRING([AtWork],1,10) >=\'2021-03-02\'and SUBSTRING([AtWork],1,10) <=\'2021-03-02\' order by  SUBSTRING([AtWork],1,10),EmployeeName