Plz help in optimizing the query

Question

I have a query which is written to cater to the scenario that the entered start and end date do not overlap with the start and end date already present in the database records. Can someone help in optimizing this query. all inclusion and exclusion scenario's have to be taken care of.
the query is as follows:
SELECT COUNT(*) FROM CLAS WHERE TRIM(UPPER(CLAS_CDE)) =UPPER('timecheck') AND TRIM(UPPER(CLAS_TYPE_CDE))=UPPER('TEST_3')
AND TRIM(UPPER(LANG_CDE))=UPPER('en')
AND (
(END_DT BETWEEN TO_DATE('09/13/2007','MM/DD/YYYY') AND TO_DATE('09/15/2007','MM/DD/YYYY'))
OR
(START_DT BETWEEN TO_DATE('09/13/2007','MM/DD/YYYY') AND TO_DATE('09/15/2007','MM/DD/YYYY'))
OR (
(START_DT BETWEEN TO_DATE('09/13/2007','MM/DD/YYYY') AND TO_DATE('09/15/2007','MM/DD/YYYY'))
AND
(END_DT BETWEEN TO_DATE('09/13/2007','MM/DD/YYYY') AND TO_DATE('09/15/2007','MM/DD/YYYY'))
OR(('09/13/2007' BETWEEN TO_CHAR(START_DT,'MM/DD/YYYY') AND TO_CHAR(END_DT,'MM/DD/YYYY'))
AND ('09/15/2007' BETWEEN TO_CHAR(START_DT,'MM/DD/YYYY') AND TO_CHAR(END_DT,'MM/DD/YYYY'))
);

Answer 1

I format your code in different way:
SELECT COUNT(*)
FROM CLAS
WHERE TRIM(UPPER(CLAS_CDE)) = UPPER('timecheck')
AND TRIM(UPPER(CLAS_TYPE_CDE))=UPPER('TEST_3')
  AND TRIM(UPPER(LANG_CDE))=UPPER('en')
   AND (
     (END_DT BETWEEN TO_DATE('09/13/2007','MM/DD/YYYY') AND TO_DATE('09/15/2007','MM/DD/YYYY'))
        OR
     (START_DT BETWEEN TO_DATE('09/13/2007','MM/DD/YYYY') AND TO_DATE('09/15/2007','MM/DD/YYYY'))
        OR (
          (START_DT BETWEEN TO_DATE('09/13/2007','MM/DD/YYYY') AND TO_DATE('09/15/2007','MM/DD/YYYY'))
          AND
          (END_DT BETWEEN TO_DATE('09/13/2007','MM/DD/YYYY') AND TO_DATE('09/15/2007','MM/DD/YYYY'))
     OR (
          ('09/13/2007' BETWEEN TO_CHAR(START_DT,'MM/DD/YYYY') AND TO_CHAR(END_DT,'MM/DD/YYYY'))
          AND
          ('09/15/2007' BETWEEN TO_CHAR(START_DT,'MM/DD/YYYY') AND TO_CHAR(END_DT,'MM/DD/YYYY'))
      );First thought that cross my mind it to check if changing this:
UPPER('timecheck') to simple:
'TIMECHECK' and do the same with other expressions with UPPER function.
Peter D.