诡异的问题

 DD07T~DOMNAME EQ 'ZD_WFTYPE'这个放在where条件和放在join条件后效果不一样 

这个是能取到值的

    SELECT
      WF_ID,
      WF_NAME,
      BEGDA,
      ENDDA,
      DD07T~DDTEXT AS WFTYPE
      INTO TABLE @DATA(LT_TABLE)
      FROM YAC_T_LIST LEFT JOIN DD07T ON YAC_T_LIST~WFTYPE EQ DD07T~VALPOS AND DD07T~DOMNAME EQ 'ZD_WFTYPE'.

这个语句取不到值

    SELECT
      WF_ID,
      WF_NAME,
      BEGDA,
      ENDDA,
      DD07T~DDTEXT AS WFTYPE
      INTO TABLE @DATA(LT_TABLE)
      FROM YAC_T_LIST LEFT JOIN DD07T ON YAC_T_LIST~WFTYPE EQ DD07T~VALPOS 
     WHERE DD07T~DOMNAME EQ 'ZD_WFTYPE'.