SQL查詢從兩類

Question

得到的記錄隨機數我有一個表：

號

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

等等

我需要得到1型和3個隨機記錄同樣數量的類型2的隨機記錄。我怎樣才能得到它與一個查詢？

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>>