我在下面执行简单的Spark-SQL代码Azure数据块。

val df2=spark.sql(
          s"""
select 
mbrgm.mbrgm_id as case_id,
      case
        when mbr_hist.meck is not null
          and mbr_hist.efdt is not null
          and mbr_hist.efdt <= mbr_pgm.credttm
          and (
            mbr_hist.exp_dt is null
             or mbr_hist.exp_dt > mbrgm.creat_dttm
          ) then mbr_hist.meck
        else mbrgm.facmbid
      end as mb_fid,
     .....
     from 
     tempview1 mbrgm 
     left join left outer join tempview2 mbr_hist on (mbrgm.mrid = mbr_hist.mrid
        and mbr_hist.efdt <= mbrgm.credttm
        and mbr_hist.exdt > mbrgm.credttm

每次我执行我得到其他条件值为mb_req字段即mbrgm. facmbid.我已经检查了我的数据，并与逻辑比较.按照逻辑，它应该去然后条件.我认为，而比较mbr_hist.efdt <= mbr_pgm.credttm它总是不正确.
我有mbr_hist.efdt作为字符串类型ex：2017-07-22 21：58：46和mbr_pgm.credttm作为时间戳ex：2011-08- 13 T11：00：00.910+0000。这是不是因为值的长度不同，我的比较失败。我可以使用什么来正确比较。