SELECT *
  FROM LCD29 L
 WHERE L.LDCD291 >= TRUNC(SYSDATE, 'dd')
   AND L.GDAB056 NOT IN
       (SELECT B.BD_DATA5
          FROM HR_COMBOOKDATE B
         WHERE B.BD_DATE >= TRUNC(SYSDATE, 'dd')
           AND TRUNC(L.LDCD291, 'dd') = TRUNC(B.BD_DATE, 'dd'));

SELECT L.*
  FROM LCD29 L
  inner join HR_COMBOOKDATE B on TRUNC(L.LDCD291, 'dd') = TRUNC(B.BD_DATE, 'dd') AND L.GDAB056 = B.BD_DATA5
 WHERE L.LDCD291 >= TRUNC(SYSDATE, 'dd')
   and B.BD_DATE >= TRUNC(SYSDATE, 'dd');

------解决方案--------------------
SELECT 1更多的时候是用在NOT EXISTS，即不存在，不存在 符合  
FROM HR_COMBOOKDATE B
  WHERE B.BD_DATE >= TRUNC(SYSDATE, 'dd')
……
这些关联条件的记录。为了迎合sql语法，需要select一个字段，那么就select 1吧，当然，select 2 也可以。