随机取 数据库中的 记录
--从一个表中随机取两条记录
--1.dbms_random.value
select * from(select * from t_ums_config order by dbms_random.value) where rownum <= 2;
--2.dbms_random.random
select * from(select * from t_ums_config order by dbms_random.random) where rownum <= 2;
--3.sys_guid()
select * from(select * from t_ums_config order by sys_guid()) where rownum <= 2;
--4.sample(20) 按百分比
select * from(select * from t_ums_config sample(20)) where rownum <= 2;
--5.sample block(20) 按数据块
select * from(select * from t_ums_config sample block(40)) where rownum <= 2;