mysql 分组后 每组随机取一条记录 求sql语句

Posted 2023-04-07

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

如何用SQL SERVER取分组数据第一条

参考技术A

根据table1_id进行分组所得结果：

select * from (select a.id as a_id,a.name,a.time,a.content,b.id as b_id,b.user from table1 a inner join table2 b on a.id = b.table1_ID) new_tbl where b_id in (select min(id) from table2 group by table1_ID)

扩展资料：

注意事项

在SQL Server数据库中，使用top关键字：SELECT TOP number|percent column_name(s) FROM table_name

在MySQL数据库中，使用LIMIT关键字：SELECT column_name(s) FROM table_name LIMIT number

例子:SELECT * FROM Persons LIMIT 1 

select   bookName   from   book   where   price   >   20   limit   1; 

limit   1;
or
limit   0,1;

在Oracle数据库中，使用ROWNUM关键字：

SELECT column_name(s) FROM table_name WHERE ROWNUM <= number

例子:SELECT * FROM Persons WHERE ROWNUM <= 1