如何一条sql语句取出分组数据中值最大的

--按某一字段分组取最大(小)值所在行的数据(2007-10-23于浙江杭州)
/*
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
*/
create table tb(id1 int,id2 int,a int,b int ,c int)
insert into tb values(1, 1, 5, 4, 3) 
insert into tb values(2, 1, 8, 6, 4) 
insert into tb values(1, 2, 6, 7, 2) 
insert into tb values(2, 2, 10, 5, 4) 
insert into tb values(1, 3, 10, 1, 1) 
insert into tb values(2, 3, 12, 2, 2)
go

--方法1：
select a.* from tb a where a = (select max(a) from tb where id2 = a.id2) order by a.id2
--方法2：
select a.* from tb a where not exists(select 1 from tb where id2 = a.id2 and a > a.a) order by a.id2
--方法3：
select a.* from tb a,(select id2,max(a) a from tb group by id2) b where a.id2 = b.id2 and a.a = b.a order by a.id2
--方法4：
select a.* from tb a inner join (select id2 , max(a) a from tb group by id2) b on a.id2 = b.id2 and a.a = b.a order by a.id2
--方法5
select a.* from tb a where 1 > (select count(*) from tb where id2 = a.id2 and a > a.a ) order by a.id2

drop table tb

/*
id1         id2         a           b           c           
----------- ----------- ----------- ----------- ----------- 
2           1           8           6           4
2           2           10          5           4
2           3           12          2           2

（所影响的行数为 3 行）

id1         id2         a           b           c           
----------- ----------- ----------- ----------- ----------- 
2           1           8           6           4
2           2           10          5           4
2           3           12          2           2

（所影响的行数为 3 行）

id1         id2         a           b           c           
----------- ----------- ----------- ----------- ----------- 
2           1           8           6           4
2           2           10          5           4
2           3           12          2           2

（所影响的行数为 3 行）

id1         id2         a           b           c           
----------- ----------- ----------- ----------- ----------- 
2           1           8           6           4
2           2           10          5           4
2           3           12          2           2

（所影响的行数为 3 行）

id1         id2         a           b           c           
----------- ----------- ----------- ----------- ----------- 
2           1           8           6           4
2           2           10          5           4
2           3           12          2           2

（所影响的行数为 3 行）
*/