Question

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

Answer 1

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)

Answer 2

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。

Answer 3

SELECT * FROM (SELECT * FROM tablename ORDER BY RAND()) as a GROUP BY a.type

Answer 4

select * from table order by rand() limit 0,1;

Answer 5

wangzhiqing999 ， holychuo答案均正确，但 wangzhiqing999 好象要强一点，学习了