TRUNC ( DATE, [ format ] )
 
-- date is the date to truncate.
-- format is the unit of measure to apply for truncating. 
 
-- If the format parameter is omitted, the trunc function 
-- will truncate the date to the day value, so that any hours, 
-- minutes, or seconds will be truncated off.
 
SELECT TO_CHAR(SYSTIMESTAMP) FROM dual;
 
SELECT TO_CHAR(TRUNC(SYSTIMESTAMP)) FROM dual;
 
TRUNC(TO_DATE('22-AUG-03'), 'YEAR') -- would return '01-JAN-03'
TRUNC(TO_DATE('22-AUG-03'), 'Q') -- would return '01-JUL-03'
TRUNC(TO_DATE('22-AUG-03'), 'MONTH') -- would return '01-AUG-03'
TRUNC(TO_DATE('22-AUG-03'), 'DDD') -- would return '22-AUG-03'
TRUNC(TO_DATE('22-AUG-03'), 'DAY') -- would return '17-AUG-03'
 
 
/*
Unit       Valid format parameters
Year       SYYYY, YYYY, YEAR, SYEAR, YYY, YY, Y
ISO Year   IYYY, IY, I
Quarter    Q
Month      MONTH, MON, MM, RM
Week       WW
IW         IW
W          W
Day         DDD, DD, J
Start day of the week    DAY, DY, D
Hour       HH, HH12, HH24
Minute     MI
*/