Most applications require the storage and manipulation of dates and times. Dates are quite complicated: not only are they highly formatted data, but there are myriad rules for determining valid values and valid calculations (leap days and years, daylight savings time changes, national and company holidays, date ranges, etc.). Fortunately, the Oracle database and PL/SQL provide a set of true datetime datatypes that store both date and time information using a standard, internal format.
For any datetime value, the database stores some or all of the following information:
Time zone region
Time zone hour offset from UTC
Time zone minute offset from UTC
Support for true datetime datatypes is only half the battle. You also need a language that can manipulate those values in a natural and intelligent manner—as actual dates and times. To that end, Oracle provides you with support for SQL standard interval arithmetic, datetime literals, and a comprehensive suite of functions with which to manipulate date and time information.