A datetime expression yields a value of one of the datetime data types.

datetime_expression::=

The initial expr is any expression, except a scalar subquery expression, that evaluates to a value of data type TIMESTAMP, TIMESTAMP WITH TIME ZONE, or TIMESTAMP WITH LOCAL TIME ZONE. The DATE data type is not supported. If this expr is itself a datetime_expression, then it must be enclosed in parentheses.

Datetimes and intervals can be combined according to the rules defined in Table 2-5. The three combinations that yield datetime values are valid in a datetime expression.

If you specify AT LOCAL, then Oracle uses the current session time zone.

The settings for AT TIME ZONE are interpreted as follows:

• The string '[+|-]hh:mi ' specifies a time zone as an offset from UTC. For hh, specify the number of hours. For mi, specify the number of minutes.

• DBTIMEZONE: Oracle uses the database time zone established (explicitly or by default) during database creation.

• SESSIONTIMEZONE: Oracle uses the session time zone established by default or in the most recent ALTER SESSION statement.

• time_zone_name: Oracle returns the datetime_value_expr in the time zone indicated by time_zone_name. For a listing of valid time zone region names, query the V$TIMEZONE_NAMES dynamic performance view.

  Note:

  Time zone region names are needed by the daylight saving feature. These names are stored in two types of time zone files: one large and one small. One of these files is the default file, depending on your environment and the release of Oracle Database you are using. For more information regarding time zone files and names, see Oracle Database Globalization Support Guide.

• expr: If expr returns a character string with a valid time zone format, then Oracle returns the input in that time zone. Otherwise, Oracle returns an error.

Example

The following example converts the datetime value of one time zone to another time zone:

SELECT FROM_TZ(CAST(TO_DATE('1999-12-01 11:00:00', 
      'YYYY-MM-DD HH:MI:SS') AS TIMESTAMP), 'America/New_York') 
   AT TIME ZONE 'America/Los_Angeles' "West Coast Time" 
   FROM DUAL;

West Coast Time
------------------------------------------------
01-DEC-99 08.00.00.000000 AM AMERICA/LOS_ANGELES