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按类别查处其中最大一个记录,该怎么处理

2012-04-10 
按类别查处其中最大一个记录有这样的表gIdjlId121314212223要求查处这样结果gIdjlId1423 [解决办法]--如果

按类别查处其中最大一个记录
有这样的表
gId       jlId
1             2
1             3
1             4
2             1
2             2
2             3

要求查处这样结果
gId         jlId
1               4
2               3


[解决办法]
--如果只有这两个字段,分组求max即可.
select gid , max(jlid) jlid from tb group by gid
[解决办法]
--如果有多个字段,则参考如下:

SQL code
--按某一字段分组取最大(小)值所在行的数据--(爱新觉罗.毓华(十八年风雨,守得冰山雪莲花开) 2007-10-23于浙江杭州)/*数据如下:name val memoa    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   b2b2b2b2b    4   b4b4b    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5select 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5select 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)valselect a.* from tb a where 2 > (select count(*) from tb where name = a.name and val < a.val ) order by a.name,a.valselect 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.valselect 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,a.val/*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)valselect a.* from tb a where 2 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name,a.valselect 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.valselect 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 , a.val/*name       val         memo                 ---------- ----------- -------------------- a          2           a2(a的第二个值)a          3           a3:a的第三个值b          4           b4b4b          5           b5b5b5b5b5*/--七,如果整行数据有重复,所有的列都相同。/*数据如下:name val memoa    2   a2(a的第二个值)a    1   a1--a的第一个值a    1   a1--a的第一个值a    3   a3:a的第三个值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   b2b2b2b2b    4   b4b4b    5   b5b5b5b5b5*/--在sql server 2000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')goselect * , px = identity(int,1,1) into tmp from tbselect m.name,m.val,m.memo from(  select t.* from tmp t where val = (select min(val) from tmp where name = t.name)) m where px = (select min(px) from(  select t.* from tmp t where val = (select min(val) from tmp where name = t.name)) n where n.name = m.name)drop table tb,tmp/*name       val         memo---------- ----------- --------------------a          1           a1--a的第一个值b          1           b1--b的第一个值(2 行受影响)*/--在sql server 2005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')goselect 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/*name       val         memo---------- ----------- --------------------a          1           a1--a的第一个值b          1           b1--b的第一个值(2 行受影响)*/ 


[解决办法]

SQL code
create table tb(gId int,jlId int)insert into tb values(1 , 2 )insert into tb values(1 , 3 )insert into tb values(1 , 4 )insert into tb values(2 , 1 )insert into tb values(2 , 2 )insert into tb values(2 , 3 )go--如果只有这两个字段,分组求max即可.select gid , max(jlid) jlid from tb group by gid/*gid         jlid        ----------- ----------- 1           42           3(所影响的行数为 2 行)*/--如果有多个字段,则参考如下:select t.* from tb t where jlid = (select max(jlid) from tb where gid = t.gid) order by t.gid/*gid         jlid        ----------- ----------- 1           42           3(所影响的行数为 2 行)*/select t.* from tb t where not exists (select 1 from tb where gid = t.gid and jlid > t.jlid) order by t.gid/*gid         jlid        ----------- ----------- 1           42           3(所影响的行数为 2 行)*/drop table tb
[解决办法]
SQL code
select gid , max(jlid) jlid from tb group by gid
[解决办法]
探讨

SQL code
select gid , max(jlid) jlid from tb group by gid

[解决办法]
探讨
--如果只有这两个字段,分组求max即可.
select gid , max(jlid) jlid from tb group by gid

[解决办法]
探讨
引用:

SQL code
select gid , max(jlid) jlid from tb group by gid


++最简单的方法

[解决办法]
select gid, max(jlid) from a group by gid

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