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If you don??™t specify any time values, their default
values are all zeros in the internal storage.
Youcan change the format youu se for inserting dates for an instance by changing
the NLS_DATE_FORMAT parameter for the instance. Youcan do this for a session
by using the ALTER SESSION SQL statement or for a specific value by using parameters
with the TO_DATE expression in your SQL statement.
Oracle SQL supports date arithmetic in which integers represent days and fractions
represent the fractional component represented by hours, minutes, and seconds. For
example, adding .5 to a date value results in a date and time combination 12 hours
later than the initial value. Some examples of date arithmetic are:
12-DEC-07 + 10 = 22-DEC-07
31-DEC-2007:23:59:59 + .25 = 1-JAN-2008:5:59:59
86 | Chapter 4: Oracle Data Structures
As of Oracle9i Release 2, Oracle also supports two INTERVAL datatypes, INTERVAL
YEAR TO MONTH and INTERVAL DAY TO SECOND, which are used for
storing a specific amount of time. This data can be used for date arithmetic.


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