[征集]分组取最大N条记录方法征集,及散分(新年,升星)
2009 的最后一天,升了一颗星,同时也祝大家新年快乐。
由于技术版不能散分。所以在此征集 <分组取最大N条记录>
create table t2 (
id int primary key,
gid char,
col1 int,
col2 int
) engine=myisam;
insert into t2 values
(1,'A',31,6),
(2,'B',25,83),
(3,'C',76,21),
(4,'D',63,56),
(5,'E',3,17),
(6,'A',29,97),
(7,'B',88,63),
(8,'C',16,22),
(9,'D',25,43),
(10,'E',45,28),
(11,'A',2,78),
(12,'B',30,79),
(13,'C',96,73),
(14,'D',37,40),
(15,'E',14,86),
(16,'A',32,67),
(17,'B',84,38),
(18,'C',27,9),
(19,'D',31,21),
(20,'E',80,63),
(21,'A',89,9),
(22,'B',15,22),
(23,'C',46,84),
(24,'D',54,79),
(25,'E',85,64),
(26,'A',87,13),
(27,'B',40,45),
(28,'C',34,90),
(29,'D',63,8),
(30,'E',66,40),
(31,'A',83,49),
(32,'B',4,90),
(33,'C',81,7),
(34,'D',11,12),
(35,'E',85,10),
(36,'A',39,75),
(37,'B',22,39),
(38,'C',76,67),
(39,'D',20,11),
(40,'E',81,36);
期望结果
1) N=1 取GID每组 COL2最大的记录
+----+------+------+------+
| id | gid | col1 | col2 |
+----+------+------+------+
| 6 | A | 29 | 97 |
| 15 | E | 14 | 86 |
| 24 | D | 54 | 79 |
| 28 | C | 34 | 90 |
| 32 | B | 4 | 90 |
+----+------+------+------+
2) N=3 取GID每组 COL2最大的3条记录
+----+------+------+------+
| id | gid | col1 | col2 |
+----+------+------+------+
| 6 | A | 29 | 97 |
| 11 | A | 2 | 78 |
| 36 | A | 39 | 75 |
| 32 | B | 4 | 90 |
| 2 | B | 25 | 83 |
| 12 | B | 30 | 79 |
| 28 | C | 34 | 90 |
| 23 | C | 46 | 84 |
| 13 | C | 96 | 73 |
| 24 | D | 54 | 79 |
| 4 | D | 63 | 56 |
| 9 | D | 25 | 43 |
| 15 | E | 14 | 86 |
| 25 | E | 85 | 64 |
| 20 | E | 80 | 63 |
+----+------+------+------+
注:
1)不限数据库,但请说明,比如 Oracle Database 10g 10.2 , MySQL 5.1.33
2) 不限方法, SQL语句,存储过程。