sql server 获取每一个类别中值最大的一条数据
时间:2022-03-14 10:21
/*
数据如下:
name val memo
a 2 a2(a的第二个值)
a 1 a1--a的第一个值
a 3 a3:a的第三个值
b 1 b1--b的第一个值
b 3 b3:b的第三个值
b 2 b2b2b2b2
b 4 b4b4
b 5 b5b5b5b5b5
*/
--创建表并插入数据:
create table tb( name varchar (10),val int ,memo varchar (20))
insert into tb values ( ‘a‘ , 2, ‘a2(a的第二个值)‘ )
insert into tb values ( ‘a‘ , 1, ‘a1--a的第一个值‘ )
insert into tb values ( ‘a‘ , 3, ‘a3:a的第三个值‘ )
insert into tb values ( ‘b‘ , 1, ‘b1--b的第一个值‘ )
insert into tb values ( ‘b‘ , 3, ‘b3:b的第三个值‘ )
insert into tb values ( ‘b‘ , 2, ‘b2b2b2b2‘ )
insert into tb values ( ‘b‘ , 4, ‘b4b4‘ )
insert into tb values ( ‘b‘ , 5, ‘b5b5b5b5b5‘ )
go
--一、按name分组取val最大的值所在行的数据。
--方法1:
select a.* from tb a where val = ( select max (val) from tb where name = a. name ) order by a. name
--方法2:
select a.* from tb a where not exists( select 1 from tb where name = a. name and val > a.val)
--方法3:
select a.* from tb a,( select name , max (val) val from tb group by name ) b where a. name = b. name and a.val = b.val order by a. name
--方法4:
select a.* from tb a inner join ( select name , max (val) val from tb group by name ) b on a. name = b. name and a.val = b.val order by a. name
--方法5
select a.* from tb a where 1 > ( select count (*) from tb where name = a. name and val > a.val ) order by a. name
/*
name val memo
---------- ----------- --------------------
a 3 a3:a的第三个值
b 5 b5b5b5b5b5
*/
|
写法6
SELECT * FROM ( SELECT * , ROW_NUMBER() OVER ( PARTITION BY name ORDER BY val DESC ) rid FROM tb ) AS t WHERE rid = 1
如果上述存在一个name组中有两个以上相同的val,则查询方法1-5不正确。
例如:
insert into tb values(‘a‘, 2, ‘a2(a的第二个值)‘)
insert into tb values(‘a‘, 3, ‘a1--a的第一个值‘)
insert into tb values(‘a‘, 3, ‘a3:a的第三个值‘)