Oracle/PLSQL: Trunc 函数截取时间格式的用法

In Oracle/PLSQL, the trunc function returns a date truncated to a specific unit of measure.

The syntax for the trunc function is:

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.

Below are the valid format parameters:

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

For example:

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'