先看一下本示例中需要使用到的数据
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');
insert into tb values('a', 1, 'a1');
insert into tb values('a', 3, 'a3');
insert into tb values('b', 1, 'b1');
insert into tb values('b', 3, 'b3');
insert into tb values('b', 2, 'b2');
insert into tb values('b', 4, 'b4');
insert into tb values('b', 5, 'b5');数据表如下：
| name | val | memo |
| a | 2 | a2 |
| a | 1 | a1 |
| a | 3 | a3 |
| b | 1 | b1 |
| b | 3 | b3 |
| b | 2 | b2 |
| b | 4 | b4 |
| b | 5 | b5 |
按name分组取val最大的值所在行的数据
方法一：
select a.* from tb a where val = (select max(val) from tb where name = a.name) order by a.name方法二：
select a.* from tb a where not exists(select 1 from tb where name = a.name and val > a.val)方法三：
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方法四：
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方法五：
select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name以上五种方法运行的结果均为如下所示：
| name | val | memo |
| a | 3 | a3 |
| b | 5 | b5 |
小编推荐使用第一、第三、第四钟方法,结果显示第1,3,4种方法效率相同，第2，5种方法效率差些。
按name分组取val最小的值所在行的数据
方法一：
select a.* from tb a where val = (select min(val) from tb where name = a.name) order by a.name方法二：
select a.* from tb a where not exists(select 1 from tb where name = a.name and val < a.val)方法三：
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方法四：
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方法五：
select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val < a.val) order by a.name以上五种方法运行的结果均为如下所示：
| name | val | memo |
| a | 1 | a1 |
| b | 1 | b1 |
按name分组取第一次出现的行所在的数据
sql如下：
select a.* from tb a where val = (select top 1 val from tb where name = a.name) order by a.name结果如下：
| name | val | memo |
| a | 2 | a2 |
| b | 1 | b1 |
按name分组随机取一条数据
sql如下：
select a.* from tb a where val = (select top 1 val from tb where name = a.name order by newid()) order by a.name结果如下：
| name | val | memo |
| a | 1 | a1 |
| b | 3 | b3 |
按name分组取最小的两个(N个)val
第一种方法：
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第二种方法：
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第三种方法：
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结果如下：
| name | val | memo |
| a | 1 | a1 |
| a | 2 | a2 |
| b | 1 | b1 |
| b | 2 | b2 |
按name分组取最大的两个(N个)val
第一种方法：
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第二种方法：
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第三种方法：
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结果如下：
| name | val | memo |
| a | 3 | a3 |
| a | 2 | a2 |
| b | 5 | b5 |
| b | 4 | b4 |