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/* 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‘)