Trunc Function (with dates)
In Oracle/PLSQL, the trunc function returns a date truncated to a specific unit of measure.
oracle中，trunc函数返回一个按照特定计量单位截取后的date值
The syntax for the trunc function is:
语法如下：
trunc ( dat1e, [ format ] )
da1te is the date to truncate.
da1te是要截断的date
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.
format 是截取时依据的计量单位(类似于数字中的精度)。如果format省略，date1就返回当天的日期值,即只保留日期，时间为 0:00:00
Below are the valid format parameters:
以下是合法的参数值：
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
Applies To:
Oracle 8i, Oracle 9i, Oracle 10g, Oracle 11g
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'
