SQL ：多条记录取最前面一条或根据条件任取N条。。。。。。

-- 按某一字段分组取最大(小)值所在行的数据

/*
数据如下：
namevalmemo
a2a2(a的第二个值)
a1a1--a的第一个值
a3a3:a的第三个值
b1b1--b的第一个值
b3b3:b的第三个值
b2b2b2b2b2
b4b4b4
b5b5b5b5b5b5
*/
-- 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 tba where val = ( select max (val) from tb where name = a.name) order by a.name
-- 方法2：
select a. * from tba where not exists ( select 1 from tb where name = a.name and val > a.val)
-- 方法3：
select a. * from tba,( 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 tba 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 tba where 1 > ( select count ( * ) from tb where name = a.name and val > a.val) order by a.name
/*
namevalmemo
-----------------------------------------
a3a3:a的第三个值
b5b5b5b5b5b5
*/

-- 二、按name分组取val最小的值所在行的数据。
-- 方法1：
select a. * from tba where val = ( select min (val) from tb where name = a.name) order by a.name
-- 方法2：
select a. * from tba where not exists ( select 1 from tb where name = a.name and val < a.val)
-- 方法3：
select a. * from tba,( 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 tba 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 tba where 1 > ( select count ( * ) from tb where name = a.name and val < a.val) order by a.name
/*
namevalmemo
-----------------------------------------
a1a1--a的第一个值
b1b1--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 tba where val = ( select top 1 val from tb where name = a.name) order by a.name
/*
namevalmemo
-----------------------------------------
a2a2(a的第二个值)
b1b1--b的第一个值
*/

-- 四、按name分组随机取一条数据。
select a. * from tba where val = ( select top 1 val from tb where name = a.name order by newid ()) order by a.name
/*
namevalmemo
-----------------------------------------
a1a1--a的第一个值
b5b5b5b5b5b5
*/

-- 五、按name分组取最小的两个(N个)val
select a. * from tba where 2 > ( select count ( * ) from tb where name = a.name and val < a.val) order by a.name,a.val
select a. * from tba 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 tba where exists ( select count ( * ) from tb where name = a.name and val < a.val having Count ( * ) < 2 ) order by a.name
/*
namevalmemo
-----------------------------------------
a1a1--a的第一个值
a2a2(a的第二个值)
b1b1--b的第一个值
b2b2b2b2b2
*/

-- 六、按name分组取最大的两个(N个)val
select a. * from tba where 2 > ( select count ( * ) from tb where name = a.name and val > a.val) order by a.name,a.val
select a. * from tba 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 tba where exists ( select count ( * ) from tb where name = a.name and val > a.val having Count ( * ) < 2 ) order by a.name
/*
namevalmemo
-----------------------------------------
a2a2(a的第二个值)
a3a3:a的第三个值
b4b4b4
b5b5b5b5b5b5
*/
-- 七，如果整行数据有重复，所有的列都相同。
/*
数据如下：
namevalmemo
a2a2(a的第二个值)
a1a1--a的第一个值
a1a1--a的第一个值
a3a3:a的第三个值
a3a3:a的第三个值
b1b1--b的第一个值
b3b3:b的第三个值
b2b2b2b2b2
b4b4b4
b5b5b5b5b5b5
*/
-- 在sqlserver2000中只能用一个临时表来解决，生成一个自增列，先对val取最大或最小，然后再通过自增列来取数据。
-- 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(a的第二个值) ' )
insert into tb values ( ' a ' , 1 , ' a1--a的第一个值 ' )
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 ( ' 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

select * ,px = identity ( int , 1 , 1 ) into tmp from tb

select m.name,m.val,m.memo from
(
select t. * from tmpt where val = ( select min (val) from tmp where name = t.name)
)m where px = ( select min (px) from
(
select t. * from tmpt where val = ( select min (val) from tmp where name = t.name)
)n where n.name = m.name)

drop table tb,tmp

/*
namevalmemo
-----------------------------------------
a1a1--a的第一个值
b1b1--b的第一个值

(2行受影响)
*/
-- 在sqlserver2005中可以使用row_number函数，不需要使用临时表。
-- 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 ' , 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 ( ' 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

select m.name,m.val,m.memo from
(
select * ,px = row_number() over ( order by name,val) from tb
)m where px = ( select min (px) from
(
select * ,px = row_number() over ( order by name,val) from tb
)n where n.name = m.name)

drop table tb

/*
namevalmemo
-----------------------------------------
a1a1--a的第一个值
b1b1--b的第一个值

(2行受影响)
*/

按按Rdate分组取num最小的值所在行的数据。并根据主从表ID左关联取主表的所有字段。。。。

select a.*,b.* from child a left join parent as b on b.id=a.PID where num = (select min(num) from child where Rdate = a.Rdate)

//三表联合查询.....

select info.PriceStartDate, Res_Golf.* from Res_Golf left join ( select Erp_GolfID,max(PriceStartDate) as PriceStartDate from Res_GolfInfo left join (select Erp_GolfInfoID,PriceStartDate from Res_GolfPrice where PriceStartDate > '2011-07-18' group by Erp_GolfInfoID,PriceStartDate ) as pri on Res_GolfInfo.GolfInfoID=pri.Erp_GolfInfoID group by Erp_GolfID) as info on Res_Golf.Erp_GolfID=info.Erp_GolfID

or

select a.Erp_GolfID, MAX(b.PriceStartDate) from Res_Golf a inner join (select a.Erp_GolfID,b.PriceStartDate from Res_GolfInfo a inner join Res_GolfPrice b on a.GolfInfoID=b.Erp_GolfInfoID group by a.Erp_GolfID,b.PriceStartDate) b on a.Erp_GolfID=b.Erp_GolfID group by a.Erp_GolfID