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6.5.1.5 Special Values
PostgreSQL supports several
special date/time input values for convenience, as shown in Table 6-13. The values
infinity and -infinity
are specially represented inside the system and will be displayed
the same way; but the others are simply notational shorthands
that will be converted to ordinary date/time values when read.
(In particular, now and related strings are converted
to a specific time value as soon as they are read.)
All of these values need to be written in single quotes when used
as constants in SQL commands.
| Input String | Valid Types | Description
|
epoch | date, timestamp | 1970-01-01 00:00:00+00 (Unix system time zero)
|
infinity | timestamp | later than all other time stamps
|
-infinity | timestamp | earlier than all other time stamps
|
now | date, time, timestamp | current transaction's start time
|
today | date, timestamp | midnight today
|
tomorrow | date, timestamp | midnight tomorrow
|
yesterday | date, timestamp | midnight yesterday
|
allballs | time | 00:00:00.00 UTC |
The following SQL-compatible functions can also
be used to obtain the current time value for the corresponding data
type:
CURRENT_DATE, CURRENT_TIME,
CURRENT_TIMESTAMP, LOCALTIME,
LOCALTIMESTAMP. The latter four accept an
optional subsecond precision specification. (See section 7.9.4 Current Date/Time.) Note however that these are
SQL functions and are not recognized as data input strings.
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