/*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*/ |
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')
