sql语句改写思路

sql优化的目标就是：用尽可能少的能量，得到同样的数据

SELECT TO_CHAR(RE.CREATION_TIME, 'yyyy-MM-dd hh24:mi:ss')
  FROM AT_PMGRADINGRECORD RE
 WHERE RE.ATR_KEY = (SELECT GRANDING_KEY_I
                       FROM (SELECT INF.GRANDING_KEY_I
                               FROM AT_TMMODULESPLINFOR INF
                              ORDER BY INF.CREATION_TIME DESC)
                      WHERE ROWNUM = 1);

改为

SELECT TO_CHAR(RE.CREATION_TIME, 'yyyy-MM-dd hh24:mi:ss')
   FROM AT_PMGRADINGRECORD RE
  WHERE RE.ATR_KEY =
        (SELECT GRANDING_KEY_I
           FROM (SELECT GRANDING_KEY_I
                   FROM AT_TMMODULESPLINFOR
                  WHERE CREATION_TIME =
                        (SELECT MAX(CREATION_TIME) FROM AT_TMMODULESPLINFOR))
          WHERE ROWNUM = 1);