SQL查询从两个类别中获取随机数量的记录

Question

我有一张桌子：

编号

id type_id
1 1
2 1
3 2
4 1
5 2
6 2
7 1
8 1
9 2

等...

我需要获得3个类型1的随机记录和相同数量的类型2的随机记录。如何通过一个查询获取它？

Answer 1

(select * from your_table where type_id = 1 order by rand() limit 3)
union all
(select * from your_table where type_id = 2 order by rand() limit 3)

Answer 2

使用MySQL

SELECT <<columns>> FROM <<table_name>>
ORDER BY RAND()
LIMIT <<count>>

使用Oracle

SELECT * FROM (SELECT * FROM <<table_name>> ORDER BY     
SYS.DBMS_RANDOM.VALUE) WHERE ROWNUM <<Count>>