--按某一欄位分組取最大(小)值所在行的資料(2007-10-23於浙江杭州)  
/*  
資料如下：  
name val memo  
a    2   a2(a的第二個值)  
a    1   a1--a的第一個值  
a    3   a3:a的第三個值  
b    1   b1--b的第一個值  
b    3   b3:b的第三個值  
b    2   b2b2b2b2  
b    4   b4b4  
b    5   b5b5b5b5b5  
*/  
--建立表並插入資料：  
create table tb(name varchar(10),val int,memo varchar
 
(20))  
insert into tb values('a',    2,   'a2(a的第二個值)')  
insert into tb values('a',    1,   'a1--a的第一個值')  
insert into tb values('a',    3,   'a3:a的第三個值')  
insert into tb values('b',    1,   'b1--b的第一個值')  
insert into tb values('b',    3,   'b3:b的第三個值')  
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分組取val最大的值所在行的資料。  
--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的第三個值  
b          5           b5b5b5b5b5  
*/  
  
--二、按name分組取val最小的值所在行的資料。  
--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的第一個值  
b          1           b1--b的第一個值  
*/  
  
--三、按name分組取第一次出現的行所在的資料。  
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的第二個值)  
b          1           b1--b的第一個值  
*/  
  
--四、按name分組隨機取一條資料。  
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的第一個值  
b          5           b5b5b5b5b5  
*/  
  
--五、按name分組取最小的兩個(N個)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的第一個值  
a          2           a2(a的第二個值)  
b          1           b1--b的第一個值  
b          2           b2b2b2b2  
*/  
  
--六、按name分組取最大的兩個(N個)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的第二個值)  
a          3           a3:a的第三個值  
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  
  
（所影響的行數為 3 行）  
  
id1         id2         a           b           c             
----------- ----------- ----------- ----------- -----------   
2           1           8           6           4  
2           2           10          5           4  
2           3           12          2           2  
  
（所影響的行數為 3 行）  
  
id1         id2         a           b           c             
----------- ----------- ----------- ----------- -----------   
2           1           8           6           4  
2           2           10          5           4  
2           3           12          2           2  
  
（所影響的行數為 3 行）  
  
id1         id2         a           b           c             
----------- ----------- ----------- ----------- -----------   
2           1           8           6           4  
2           2           10          5           4  
2           3           12          2           2  
  
（所影響的行數為 3 行）  
  
id1         id2         a           b           c             
----------- ----------- ----------- ----------- -----------   
2           1           8           6           4  
2           2           10          5           4  
2           3           12          2           2  
  
（所影響的行數為 3 行）  
*/