--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 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')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。
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.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/* 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)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.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/* name val memo ---------- ----------- -------------------- a 2 a2(a的第二个值) a 3 a3:a的第三个值 b 4 b4b4 b 5 b5b5b5b5b5*/
--七，假如整行数据有重复，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 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：
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 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')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/* 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)*/
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