Oracle 中与时间有关的计算

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# sysdate+1/24        - 加1小时# sysdate+1/24/60     - 加1分钟# sysdate+1/24/60/60  - 加1秒钟# SQL> alter session set nls_date_format='yyyy-MM-dd hh24:mi:ss';Session altered.SQL> select sysdate, sysdate+1/24, sysdate+1/24/60, sysdate+1/24/60/60 from dual;SYSDATE             SYSDATE+1/24        SYSDATE+1/24/60     SYSDATE+1/24/60/60------------------- ------------------- ------------------- -------------------2013-09-18 09:40:43 2013-09-18 10:40:43 2013-09-18 09:41:43 2013-09-18 09:40:44SQL> -- 获取本周第一天SQL> select trunc(sysdate, 'day') from dual;TRUNC(SYSDATE,'DAY'                                                             -------------------                                                             2013-10-13 00:00:00                                                             SQL> -- 获取本周最后一天SQL> select trunc(sysdate, 'day') + 7 - 1/24/60/60 from dual;TRUNC(SYSDATE,'DAY'                                                             -------------------                                                             2013-10-19 23:59:59                                                             SQL> -- 获取下周第 n 天SQL> select trunc(next_day(sysdate, 1)), trunc(next_day(sysdate, 7)) from dual;TRUNC(NEXT_DAY(SYSD TRUNC(NEXT_DAY(SYSD                                         ------------------- -------------------                                         2013-10-20 00:00:00 2013-10-26 00:00:00                                         SQL> --SQL> -- 获取上月第一天SQL> select trunc(add_months(sysdate, -1), 'month') from dual;TRUNC(ADD_MONTHS(SY                                                             -------------------                                                             2013-09-01 00:00:00                                                             SQL> select to_date(to_char(add_months(sysdate, -1), 'yyyy-MM'), 'yyyy-MM') from dual;TO_DATE(TO_CHAR(ADD                                                             -------------------                                                             2013-09-01 00:00:00                                                             SQL> -- 获取本月第一天SQL> select trunc(sysdate, 'month') from dual;TRUNC(SYSDATE,'MONT                                                             -------------------                                                             2013-10-01 00:00:00                                                             SQL> select to_date(to_char(sysdate, 'yyyy-MM'), 'yyyy-MM') from dual;TO_DATE(TO_CHAR(SYS                                                             -------------------                                                             2013-10-01 00:00:00                                                             SQL> -- 获取本月最后一天SQL> select trunc(last_day(sysdate)) + 1 - 1/24/60/60 from dual;TRUNC(LAST_DAY(SYSD                                                             -------------------                                                             2013-10-31 23:59:59                                                             SQL> select add_months(trunc(sysdate, 'month'), 1) - 1/24/60/60 from dual;ADD_MONTHS(TRUNC(SY                                                             -------------------                                                             2013-10-31 23:59:59                                                             SQL> --SQL> -- 获取本季度第一天SQL> select trunc(sysdate, 'Q') from dual;TRUNC(SYSDATE,'Q')                                                              -------------------                                                             2013-10-01 00:00:00                                                             SQL> -- 获取本季度最后一天SQL> select add_months(trunc(sysdate, 'Q'), 3) - 1/24/60/60 from dual;ADD_MONTHS(TRUNC(SY                                                             -------------------                                                             2013-12-31 23:59:59                                                             SQL> --SQL> -- 获取去年第一天(因为闰年平年天数不一样，所以不能使用加减 366或365天 来计算年份)SQL> select trunc(trunc(sysdate, 'year') - 1, 'year') from dual;TRUNC(TRUNC(SYSDATE                                                             -------------------                                                             2012-01-01 00:00:00                                                             SQL> -- 获取今年第一天SQL> select trunc(sysdate, 'year') from dual;TRUNC(SYSDATE,'YEAR                                                             -------------------                                                             2013-01-01 00:00:00                                                             SQL> select to_date(to_char(sysdate, 'yyyy')||'-01-01', 'yyyy-MM-dd') from dual;TO_DATE(TO_CHAR(SYS                                                             -------------------                                                             2013-01-01 00:00:00                                                             SQL> -- 获取今年最后一天SQL> select trunc(add_months(sysdate, 12), 'year') - 1/24/60/60 from dual;TRUNC(ADD_MONTHS(SY                                                             -------------------                                                             2013-12-31 23:59:59                                                             SQL> select to_date(to_char(sysdate, 'yyyy')||'-12-31 23:59:59', 'yyyy-MM-dd hh24:mi:ss') from dual;TO_DATE(TO_CHAR(SYS                                                             -------------------                                                             2013-12-31 23:59:59                                                             SQL> SQL> -- 计算相差的天数SQL> select round(to_number(to_date('2013-10-19 23:59:59', 'yyyy-MM-dd hh24:mi:ss') - to_date('2013-10-18 00:00:00', 'yyyy-MM-dd hh24:mi:ss'))) value from dual;     VALUE                                                                      ----------                                                                               2                                                                      SQL> -- 计算相差的小时数SQL> select round(to_number(to_date('2013-10-19 12:00:00', 'yyyy-MM-dd hh24:mi:ss') - to_date('2013-10-19 11:00:00', 'yyyy-MM-dd hh24:mi:ss')) * 24) value from dual;     VALUE                                                                      ----------                                                                               1                                                                      SQL> -- 计算相差的分钟数SQL> select round(to_number(to_date('2013-10-19 12:00:00', 'yyyy-MM-dd hh24:mi:ss') - to_date('2013-10-19 11:30:00', 'yyyy-MM-dd hh24:mi:ss')) * 24 * 60) value from dual;     VALUE                                                                      ----------                                                                              30                                                                      SQL>
# 相关链接
ROUND(date) http://docs.oracle.com/cd/E11882_01/server.112/e41084/functions154.htm#SQLRF00699
TRUNC(date) http://docs.oracle.com/cd/E11882_01/server.112/e41084/functions220.htm#SQLRF06151