select floor(sysdate-max(dt)) workingDays
from(
select distinct dt, 
(case when (select count(*) 
from leave_staff_trx where date_trx = t1.dt and staff_no = '1024') > 0
then 1 else 0 end) cnt
from(select trunc(sysdate) as DT from dual 
union
SELECT TRUNC (SYSDATE-rownum) dt FROM DUAL CONNECT BY ROWNUM < 30) t1
order by 1 desc) x1
where cnt =0;

SELECT Floor(SYSDATE - Max(dt)) workingDays
FROM  (SELECT DISTINCT dt,
                       ( CASE
                           WHEN (SELECT Count(*)
                                 FROM   leave_staff_trx
                                 WHERE  date_trx = t1.dt
                                        AND staff_no = '1024') > 0 THEN 1
                           ELSE 0
                         END ) cnt
       FROM  (SELECT Trunc(SYSDATE) AS DT
              FROM   dual
              UNION
              SELECT Trunc (SYSDATE - ROWNUM) dt
              FROM   dual
              CONNECT BY ROWNUM < 30) t1
       ORDER  BY 1 DESC) x1
WHERE  cnt = 0; 

with
  t1 as (     SELECT Trunc(SYSDATE) AS DT
              FROM   dual
              UNION
              SELECT Trunc (SYSDATE - ROWNUM) dt
              FROM   dual
              CONNECT BY ROWNUM < 30
        ),
  cnt (       SELECT t1.dt, nvl2(Count(*),1,0) cnt
              FROM   t1 left outer join leave_staff_trx on date_trx = t1.dt
              WHERE  staff_no = '1024'
              group by t1.dt
      )
SELECT Floor(SYSDATE - Max(dt)) workingDays
from cnt
WHERE  cnt = 0

SQL> with
  2    t1 as (     SELECT Trunc(SYSDATE) AS DT
  3                FROM   dual
  4                UNION
  5                SELECT Trunc (SYSDATE - ROWNUM) dt
  6                FROM   dual
  7                CONNECT BY ROWNUM < 30
  8          )
  9  SELECT Floor(SYSDATE - Max(dt)) workingDays
 10  from t1
 11  /
WORKINGDAYS
-----------
          0

select 0 workingDays 
from dual
where not exists ( select null from leave_staff_trx 
                   where staff_no = '1024'
                   and date_trx >= trunc(sysdate-30)

SQL> select floor(sysdate-max(dt)) workingDays
  2  from(
  3  select distinct dt,
  4  (case when (select count(*) from leave_staff_trax where date_trx = t1.dt and badge = '201414') > 0 then 1 else 0 end) cnt
  5  from(select trunc(sysdate) as DT from dual union SELECT TRUNC (SYSDATE-rownum) dt FROM DUAL CONNECT BY ROWNUM < 30) t1
  6  order by 1 desc) x1
  7  where cnt =0;
WORKINGDAYS
-----------
          4

SQL> SELECT Floor(SYSDATE - Max(dt)) workingDays
  2  FROM  (SELECT DISTINCT dt,
  3                         ( CASE
  4                             WHEN (SELECT Count(*)
  5                                   FROM   leave_staff_trax
  6                                   WHERE  date_trx = t1.dt
  7                                          AND badge = 201414) > 0 THEN 1
  8                             ELSE 0
  9                           END ) cnt
 10         FROM  (SELECT Trunc(SYSDATE) AS DT
 11                FROM   dual
 12                UNION
 13                SELECT Trunc (SYSDATE - ROWNUM) dt
 14                FROM   dual
 15                CONNECT BY ROWNUM < 30) t1
 16         ORDER  BY 1 DESC) x1
 17  WHERE  cnt = 0
 18  /
WORKINGDAYS
-----------
          4

SQL> with
  2    t1 as (     SELECT Trunc(SYSDATE) AS DT
  3                FROM   dual
  4                UNION
  5                SELECT Trunc (SYSDATE - ROWNUM) dt
  6                FROM   dual
  7                CONNECT BY ROWNUM < 30
  8          ),
  9    cnt as (    SELECT t1.dt, Count(date_trx) cnt
 10                FROM   t1 left outer join
 11                        ( select * from LEAVE_STAFF_TRAX where badge = 201414 )
 12                         on date_trx = t1.dt
 13               group by t1.dt order by t1.dt
 14        )
 15  SELECT Floor(SYSDATE - Max(dt)) workingDays
 16  from cnt
 17  WHERE  cnt = 0
 18  /
WORKINGDAYS
-----------
          4

SQL> with
  2    data as (
  3      select BADGE, DATE_TRX,
  4             lead(DATE_TRX) over (partition by BADGE order by DATE_TRX desc) prev_date,
  5             max(DATE_TRX) over (partition by badge) last_day
  6      from LEAVE_STAFF_TRAX
  7      where DATE_TRX >= trunc(sysdate-30)
  8    )
  9  select badge,
 10         case when last_day = trunc(sysdate) then trunc(sysdate)-max(date_trx)+1
 11              else 0
 12         end workingDays
 13  from data
 14  where prev_date != date_trx-1
 15  group by badge, last_day
 16  order by badge
 17  /
     BADGE WORKINGDAYS
---------- -----------
     39496           0
     40386           0
    201414           4
    470346           2
    543789           3

SQL> with
  2    data as (
  3      select BADGE, DATE_TRX,
  4             lead(DATE_TRX) over (order by DATE_TRX desc) prev_date,
  5             max(DATE_TRX) over () last_day
  6      from LEAVE_STAFF_TRAX
  7      where badge = 201414 and DATE_TRX >= trunc(sysdate-30)
  8    )
  9  select case when last_day = trunc(sysdate) then trunc(sysdate)-max(date_trx)+1
 10              else 0
 11         end workingDays
 12  from data
 13  where prev_date != date_trx-1
 14  group by last_day
 15  /
WORKINGDAYS
-----------
          4

SQL> select case when last_day = trunc(sysdate) then trunc(sysdate)-max(date_trx)+1
  2              else 0
  3         end workingDays
  4  from ( select BADGE, DATE_TRX,
  5                lead(DATE_TRX) over (order by DATE_TRX desc) prev_date,
  6                max(DATE_TRX) over () last_day
  7         from LEAVE_STAFF_TRAX
  8         where badge = 201414 and DATE_TRX >= trunc(sysdate-30) ) data
  9  where prev_date != date_trx-1
 10  group by last_day
 11  /
WORKINGDAYS
-----------
          4

1 row selected.

SQL> SELECT Floor(SYSDATE - Max(dt)) workingDays
  2  from ( SELECT t1.dt, Count(date_trx) cnt
  3         FROM   ( SELECT Trunc(SYSDATE) AS DT
  4                  FROM   dual
  5                  UNION
  6                  SELECT Trunc (SYSDATE - ROWNUM) dt
  7                  FROM   dual
  8                  CONNECT BY ROWNUM < 30 ) t1
  9                left outer join
 10                ( select * from LEAVE_STAFF_TRAX where badge = 201414 )
 11                on date_trx = t1.dt
 12         group by t1.dt order by t1.dt ) cnt
 13  WHERE  cnt = 0
 14  /
WORKINGDAYS
-----------
          4

1 row selected.

SQL> Insert into LEAVE_STAFF_TRAX
  2     (DATE_TRX, BADGE)
  3   Values
  4     (TO_DATE('03/30/2017 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), 201414);

1 row created.

SQL> commit;

Commit complete.

SQL> SELECT Floor(SYSDATE - Max(dt)) workingDays
  2  from ( SELECT t1.dt, Count(date_trx) cnt
  3         FROM   ( SELECT Trunc(SYSDATE) AS DT
  4                  FROM   dual
  5                  UNION
  6                  SELECT Trunc (SYSDATE - ROWNUM) dt
  7                  FROM   dual
  8                  CONNECT BY ROWNUM < 30 ) t1,
  9                ( select * from LEAVE_STAFF_TRAX where badge = 201414 )
 10         where date_trx (+) = t1.dt
 11         group by t1.dt ) cnt
 12  WHERE  cnt = 0
 13  /
WORKINGDAYS
-----------
          5

1 row selected.