使用随机时间戳更新多行

Question

我试图用随机时间戳更新列的多行但是再次 所有行都使用相同的时间戳进行更新。

UPDATE RCBDBA.RCORD_REC S  
   SET R_TMSTMP= (
    SELECT to_timestamp(sysdate-201)  
          + (dbms_random.value(1,8))
          + (dbms_random.value(0,31))
          + (dbms_random.value(0,24)/24)
          + (dbms_random.value(0,1440)/1440)
          + (dbms_random.value(0,86400)/86400) AS ran 
     FROM dual) 
 WHERE S.WS_ID IN (
   SELECT S.WS_ID 
     FROM RCBDBA.RCORD_REC S 
    WHERE S.R_TMSTMP IN TO_TIMESTAMP ((
   SELECT scr.R_TMSTMP 
     FROM RCBDBA.RCORD_REC scr 
    GROUP BY scr.R_TMSTMP 
   HAVING COUNT(*) =177 )) )