select * from tb t where datetime=(select max(datetime) from tb where bookid=t.bookid)

------解决方案--------------------
SQL code
select * from tb t where [datetime]=(select max([datetime]) from tb where bookid=t.bookid)

------解决方案--------------------
SQL code
select A.*
from TB A
where not exists(select 1 from TB B where A.booksid = B.booksid and A.datetime <B.datetime)

------解决方案--------------------
select b.booksid,b.datetime from table as b join
(
select booksid,max(datetime) from table as A group by booksid) as c
on b.booksid=c.booksid and b.datetime=c.datetime

ls几位的也可以的,很多种办法

------解决方案--------------------
select b.booksid,b.datetime from table as b join
(
select booksid,max(datetime)as datetime from table as A group by booksid) as c
on b.booksid=c.booksid and b.datetime=c.datetime

------解决方案--------------------

SQL code

create table ny
(booksid int,dt time)  

insert into ny
select 1, '10:00:00' union all
select 1, '12:00:00' union all
select 2, '07:00:00' union all
select 2, '11:00:00'


select booksid,dt
from
(select *,row_number() over(partition by booksid order by dt desc) rn
 from ny) y
where rn=1

/*
booksid     dt
----------- ----------------
1           12:00:00.0000000
2           11:00:00.0000000

(2 row(s) affected)
*/