/* 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 */
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写法6
SELECT * FROM ( SELECT * , ROW_NUMBER() OVER ( PARTITION BY name ORDER BY val DESC ) rid FROM tb ) AS t WHERE rid = 1
如果上述存在一个name组中有两个以上相同的val，则查询方法1-5不正确。
例如：
insert into tb values(‘a‘, 2, ‘a2(a的第二个值)‘)
insert into tb values(‘a‘, 3, ‘a1--a的第一个值‘)
insert into tb values(‘a‘, 3, ‘a3:a的第三个值‘)