按某一字段分组取最大(小)值所在行的数据

--按某一字段分组取最大(小)值所在行的数据


/*

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

*/



--二、按name分组取val最小的值所在行的数据。

--方法1：

select a.* from tb
a where val = (select min(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,min(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 , min(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
1 a1--a的第一个值

b
1 b1--b的第一个值

*/



--三、按name分组取第一次出现的行所在的数据。

select a.* from tb a where val
= (select top 1 val
from tb where name = a.name) order by a.name

/*

name val
memo


---------- ----------- --------------------

a
2 a2(a的第二个值)

b
1 b1--b的第一个值

*/



--四、按name分组随机取一条数据。

select a.* from tb
a where val = (select top 1 val from tb
where name = a.name
order by newid()) order by a.name

/*

name val
memo


---------- ----------- --------------------

a
1 a1--a的第一个值

b
5 b5b5b5b5b5

*/



--五、按name分组取最小的两个(N个)val

select a.* from tb
a where 2 > (select count(*) from tb
where name = a.name
and val < a.val ) order by a.name,a.val

select a.* from tb
a where val in (select top 2 val from tb
where name=a.name order by val) order by a.name,a.val

select a.* from tb
a where exists (select count(*) from tb
where name = a.name
and val < a.val having Count(*) < 2) order by a.name

/*

name val
memo


---------- ----------- --------------------

a 1
a1--a的第一个值

a
2 a2(a的第二个值)

b
1 b1--b的第一个值

b
2 b2b2b2b2

*/



--六、按name分组取最大的两个(N个)val

select a.* from tb
a where 2 > (select count(*) from tb
where name = a.name
and val > a.val ) order by a.name,a.val

select a.* from tb
a where val in (select top 2 val from tb
where name=a.name order by val desc) order by a.name,a.val

select a.* from tb
a where exists (select count(*) from tb
where name = a.name
and val > a.val having Count(*) < 2) order by a.name

/*

name val
memo


---------- ----------- --------------------

a
2 a2(a的第二个值)

a
3 a3:a的第三个值

b
4 b4b4

b
5 b5b5b5b5b5