各数据库分页sql备忘

ORACLE
下面这个效率很低
SELECT * FROM ( SELECT A.*, ROWNUM RN FROM (SELECT * FROM IPAY_RCD_FS_RETURN order by id desc) A ) WHERE RN <20;
下面这个效率很高
SELECT A.*, ROWNUM RN FROM (SELECT * FROM IPAY_RCD_FS_RETURN order by id desc) A WHERE ROWNUM <= 20;


完整分页语句：
SELECT * FROM
(
SELECT A.*, ROWNUM RN
FROM (SELECT * FROM TABLE_NAME) A
WHERE ROWNUM <= 40
)
WHERE RN >= 21