从表中随机返回n条记录

CREATE OR REPLACE VIEW V AS
SELECT 'a' AS c FROM dual
UNION ALL
SELECT 'b' AS c FROM dual
UNION ALL
SELECT 'c' AS c FROM dual
UNION ALL
SELECT 'd' AS c FROM dual
UNION ALL
SELECT 'e' AS c FROM dual;
SELECT * FROM v;

SELECT c
  FROM (SELECT c FROM v ORDER BY DBMS_RANDOM.VALUE())
 WHERE ROWNUM < 3;