大家好，我遇到一个疑问，就是排序的时候是按三个变量排，但是set by 的时候只取开头和最后的变量，这样的程序我以前跑没问题，但是最近一次跑，总提示出现错误，说set by的变量没有排列好？这是什么原因呢？谢谢帮忙！


proc sql;
  CREATE TABLE alert_p3 AS
  SELECT
    a.medicaid_num,
    b.PCP_PROVIDER_ID_2001_3 AS pcp_provider_id,
    c.provider_name_2003 AS managed_care_plan_name,
    datepart(b.DATE_BEGIN_PCP_3331_1) AS Date_Begin_PCP format = mmddyy10.,
    datepart(b.DATE_END_PCP_3331_2) AS Date_End_PCP format = mmddyy10.
  FROM
    high.c_age_medicare a
  INNER JOIN
    DM_med.omh_recip_prepaid_cap_date b ON
/*   medicaid.omh_recip_prepaid_cap_date b */
      a.medicaid_num = b.recipient_id_1010
  INNER JOIN
    DM_med.DIM_MCAID_PROV_CURRENT c ON
    /* medicaid.provider_current c  */
      b.PCP_PROVIDER_ID_2001_3 = c.provider_id_2001
  WHERE
    Pcp_Capitation_Code_3330 <> '0' AND
    DATE_BEGIN_PCP_3331_1 < &enddt. AND
    DATE_END_PCP_3331_2 >= &enddt.
  ORDER BY
    medicaid_num,
    DATE_BEGIN_PCP_3331_1,
    DATE_END_PCP_3331_2;
quit;

* Take the most recent pcp dates;
data alert_plan_eligib_p3;
   set alert_p3;
   by Medicaid_num date_end_pcp;
   if last.medicaid_num=1;
run;

ERROR: BY variables are not properly sorted on data set
       WORK.ALERT_P3.