Help in date function

Question

can some one tell the difference between the given 2 sql statements .
1.trunc(ps.DISCH_DTTM) - trunc(ps.admit_dttm) >= 2
and
2. (ps.DISCH_DTTM - ps.admit_dttm) >= 2
which one will give me the result which has more then or equal to 48 hours of time period that is complete 2 days .
Thanks In advance .

Answer 1

Why not try out the different variants?
WITH t1 AS (SELECT TO_DATE('01.01.2006 00:00', 'dd.mm.yyyy hh24:mi') + ((ROWNUM - 1) / 24) beg_date
              FROM user_objects
             WHERE ROWNUM <= 3),
     t2 AS (SELECT 2 + ((ROWNUM - 3) / (24 * 60)) days            
              FROM user_objects
             WHERE ROWNUM <= 4)
SELECT ps.*,
       TRUNC(ps.DISCH_DTTM) - TRUNC(ps.admit_dttm) v1,
       (ps.DISCH_DTTM - ps.admit_dttm) v2
  FROM (SELECT beg_date admit_dttm, days * 24 hours, beg_date + days disch_dttm
          FROM t1, t2
       ) ps
;That should give you a test case and an idea what results you can expect with the different versions of date subtraction.
C.