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/*
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www.111Cn.net ' )
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www.111com.net。
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
*/
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