mysql分组后，取每组的前3条数据（并且有顺序）

Posted 2023-05-02

就是首先分组，然后取出每组前3条数据，每组内的数据是排序的

不列出表结构及测试数据,只能这样大概写个思路了:

select a.*
from
(
select t1.*,(select count(*)+1 from 表 where 分组字段=t1.分组字段 and 排序字段<t1.排序字段) as group_id
from 表 t1
) a
where a.group_id<=3 参考技术A select *
from tb k
where 3>(select count(*) from tb where k.分组字段=分组字段 and 你的排序字段>k.你的排序字段)

mysql 分组后 每组随机取一条记录 求sql语句

如题，大家帮我想想SQL语句怎么写，数据库是mysql
如下表：
id type str
1 0 aaa
2 0 bbb
3 1 sss
4 1 ddd
5 2 ggg
6 2 hhh
比如我把表里的记录按type分成3组，每组要随机出一条记录，那么我要的结果就是3条type不同的随机的记录。关键是随机，不是max、min

CREATE TABLE test_gd2gd2(
id INT,
type INT,
str CHAR(3)
);

INSERT INTO test_gd2gd2
SELECT 1, 0, 'aaa' UNION ALL
SELECT 2, 0, 'bbb' UNION ALL
SELECT 3, 1, 'sss' UNION ALL
SELECT 4, 1, 'ddd' UNION ALL
SELECT 5, 2, 'ggg' UNION ALL
SELECT 6, 2, 'hhh';

mysql> SELECT
-> type,
-> (SELECT str FROM test_gd2gd2 sub
-> WHERE type = main.type ORDER BY rand()
-> LIMIT 0,1) AS Rstr
-> FROM
-> test_gd2gd2 main
-> GROUP BY
-> type;
+------+------+
| type | Rstr |
+------+------+
| 0 | bbb |
| 1 | ddd |
| 2 | hhh |
+------+------+
3 rows in set (0.01 sec)

mysql> SELECT
-> type,
-> (SELECT str FROM test_gd2gd2 sub
-> WHERE type = main.type ORDER BY rand()
-> LIMIT 0,1) AS Rstr
-> FROM
-> test_gd2gd2 main
-> GROUP BY
-> type;
+------+------+
| type | Rstr |
+------+------+
| 0 | aaa |
| 1 | sss |
| 2 | hhh |
+------+------+
3 rows in set (0.00 sec) 参考技术A 在sqlserver中用的是top关键字 比如查询user表
select * from user limit 1 ;这就可以了，， 另外 mysql 中的翻页很方便的。比sqlserver中的简单多了。
参考技术B SELECT * FROM (SELECT * FROM tablename ORDER BY RAND()) as a GROUP BY a.type 参考技术C select * from table order by rand() limit 0,1; 参考技术D wangzhiqing999 ， holychuo答案均正确，但 wangzhiqing999 好象要强一点，学习了