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按某一字段分组取最大(小)值所在行的数据 数据如下： name val memo a 1 a1 a 2 a2 a 3 a3 b 1 b1 b 2 b2 b 3 b3 b 4 b4 b 5 b5 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 bya.name 方法2： select a.* from tb a where notexists(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) bwherea.name=b.nameanda.val=b.valorder bya.name 方法4： select a.* fromtb a inner join(select name,max(val) val from tb group by name) bona.name=b.nameanda.val=b.valorderbya.name 方法5 select a.* fromtb a where 1>(select count (*) from tb where name=a.name and val>a.val )order bya.name name val memo a 3 a3 b 5 b5 二、按name分组取val最小的值所在行的数据。 方法1： select a.*fromtb a where val=(select min(val)from tb where name=a.name)order bya.name 方法2： select a.*fromtb a where not exists(select 1 from tb where name=a.name and val<a.val) 方法3： select a.*fromtb a,(select name,min(val)val from tb group by name) bwherea.name=b.nameanda.val=b.valorder bya.name 方法4： select a.*fromtb a inner join(select name,min(val) val from tb group by name) bona.name=b.nameanda.val=b.valorderbya.name 方法5 select a.*fromtb a where 1>(select count (*) from tb where name=a.name and val<a.val)order bya.name name val memo a 1 a1 b 1 b1 三、按name分组取第一次出现的行所在的数据。 select a.*fromtb a where val=(select top1 val from tb where name=a.name)order bya.name name val memo a 2 a2 b 1 b1 四、按name分组随机取一条数据。 select a.*fromtb a where val=(select top1 val from tb where name=a.name order by newid())order bya.name name val memo a 1 a1 b 5 b5 五、按name分组取最小的两个(N个)val select a.*fromtb a where 2>(select count (*) from tb where name=a.name and val<a.val )order bya.name,a.val select a.*fromtb a where valin(select top2 val from tb where name=a.name order by val)order bya.name,a.val select a.*fromtb awhere exists(select count (*) from tb where name=a.name and val<a.valhavingCount(*)<2)orderbya.name name val memo a 1 a1 a 2 a2 b 1 b1 b 2 b2 六、按name分组取最大的两个(N个)val select a.*fromtb a where 2>(select count (*) from tb where name=a.name and val>a.val )order bya.name,a.val 提取出每行的name 和val 去数据库中找比自己小的个数。如果小于2个，代表自己就是满足条件的 select a.*from tb a where val in (select top2 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 havingCount(*) <2)order by a.name name val memo a 2 a2 a 3 a3 b 4 b4b4 b 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 memo a 2 a2 a 1 a1 a 1 a1 a 3 a3 a 3 a3 b 1 b1 b 3 b3 b 2 b2b2b2b2 b 4 b4b4 b 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：
select* , px =identity(int,1,1) into tmpfrom tb
select 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 b 1 b1 (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),valint,memo varchar(20)) insert into tb values('a', 2, 'a2') insert into tb values('a', 1, 'a1') insert into tb values('a', 1, 'a1') insert into tb values('a', 3, 'a3') 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, '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 byname , val) from tb) m where px = (select min(px) from (select* , px = row_number() over(order byname , val) from tb) n where n.name = m.name) drop table tb name val memo a 1 a1 b 1 b1 (2 行受影响) |