本节介绍了基本算术操作符（+，-）的功能和可以用于处理日期/时间类型值的函数。
表 2显示了所有可以用于处理日期/时间类型值的函数，关于这些函数的更详细信息将在后面的部分中出现。在表 1中说明了基本算术操作符（+，-）的功能。对于格式化类型的函数，请参见用于各种数据类型的格式化函数。在进行本节的内容学习前，应该从章节日期/时间类型中熟悉了日期/时间类型的背景信息。
| Operator | Example | Result |
|---|---|---|
| + | DATE '2001-09-28' + 7 | 05-OCT-01 00:00:00 |
| + | TIMESTAMP '2001-09-28 13:30:00' + 3 | 01-OCT-01 13:30:00 |
| - | DATE '2001-10-01' - 7 | 24-SEP-01 00:00:00 |
| - | TIMESTAMP '2001-09-28 13:30:00' - 3 | 25-SEP-01 13:30:00 |
| - | TIMESTAMP '2001-09-29 03:00:00' - TIMESTAMP '2001-09-27 12:00:00' | @ 1 day 15 hours |
在表 2中显示的日期/时间函数中，DATE和TIMESTAMP数据类型可以互换使用。
| Function | Return Type | Description | Example | Result |
|---|---|---|---|---|
| ADD MONTHS(DATE, NUMBER) | DATE | Add months to a date. | ADD MONTHS('28-FEB-97', 3.8) | 31-MAY-97 00:00:00 |
| CURRENT DATE | DATE | Current date. | CURRENT DATE | 04-JUL-07 |
| CURRENT TIMESTAMP | TIMESTAMP | Returns the current date and time. | CURRENT TIMESTAMP | 04-JUL-07 15:33:23.484 |
| EXTRACT(field FROM TIMESTAMP) | DOUBLE PRECISION | Get subfield. | EXTRACT(hour FROM TIMESTAMP '2001-02-16 20:38:40') | 20 |
| LAST DAY(DATE) | DATE | Returns the last day of the month represented by the given date. If the given date contains a time portion, it is carried forward to the result unchanged. | LAST DAY('14-APR-98') | 30-APR-98 00:00:00 |
| LOCALTIMESTAMP [ (precision) ] | TIMESTAMP | Current date and time (start of current transaction). | LOCALTIMESTAMP | 04-JUL-07 15:33:23.484 |
| MONTHS BETWEEN(DATE, DATE) | NUMBER | Number of months between two dates. | MONTHS BETWEEN('28-FEB- 07', '30-N0V-06') | 3 |
| NEXT DAY(DATE, dayofweek) | DATE | Date falling on dayofweek following specified date. | NEXT DAY('16-APR- 07','FRI') | 2 0-APR-07 00:00:00 |
| NEW TIME(DATE, VARCHAR, VARCHAR) | DATE | Converts a date and time to an alternate time zone | NEW TIME(T0 DATE '2005/05/29 01:45', 'AST', 'PST') | 2005/05/29 21:45:00 |
| ROUND(DATE [, format ]) | DATE | Date rounded according to format. | R0UND(T0 DATE('29-MAY- 05'),'M0N') | 01-JUN-05 00:00:00 |
| SYS EXTRACT UTC(TIME STAMP WITH TIME ZONE) | TIMESTAMP | TIMESTAMP | SYS EXTRACT UTC(CAST('24 -MAR-11 12:30:00PM - 04:00' AS TIMESTAMP WITH TIME ZONE)) | 2 4-MAR-11 16:30:00 |
| SYSDATE | DATE | Returns current date and time | SYSDATE | 01-AUG-12 11:12:34 |
| SYSTIMESTAMP() | TIMESTAMP | Returns current date and time | SYSTIMESTAMP | 01-AUG-12 11:11:23.665 229 -07:00 |
| TRUNC(DATE [format ]) | DATE | Truncate according to format. | TRUNC(T0 DATE('2 9-MAY- 05'), 'MON') | 01-MAY-05 00:00:00 |