Provided by: libdatetime-format-pg-perl_0.16009-1_all 
NAME
DateTime::Format::Pg - Parse and format PostgreSQL dates and times
SYNOPSIS
use DateTime::Format::Pg;
my $dt = DateTime::Format::Pg->parse_datetime( '2003-01-16 23:12:01' );
# 2003-01-16 23:12:01
DateTime::Format::Pg->format_datetime($dt);
DESCRIPTION
This module understands the formats used by PostgreSQL for its DATE, TIME, TIMESTAMP, and INTERVAL data
types. It can be used to parse these formats in order to create "DateTime" or "DateTime::Duration"
objects, and it can take a "DateTime" or "DateTime::Duration" object and produce a string representing it
in a format accepted by PostgreSQL.
CONSTRUCTORS
The following methods can be used to create "DateTime::Format::Pg" objects.
• new( name => value, ... )
Creates a new "DateTime::Format::Pg" instance. This is generally not required for simple operations.
If you wish to use a different parsing style from the default then it is more comfortable to create
an object.
my $parser = DateTime::Format::Pg->new()
my $copy = $parser->new( 'european' => 1 );
This method accepts the following options:
• european
If european is set to non-zero, dates are assumed to be in european dd/mm/yyyy format. The
default is to assume US mm/dd/yyyy format (because this is the default for PostgreSQL).
This option only has an effect if PostgreSQL is set to output dates in the 'PostgreSQL' (DATE
only) and 'SQL' (DATE and TIMESTAMP) styles.
Note that you don't have to set this option if the PostgreSQL server has been set to use the
'ISO' format, which is the default.
• server_tz
This option can be set to a "DateTime::TimeZone" object or a string that contains a time zone
name.
This value must be set to the same value as the PostgreSQL server's time zone in order to
parse TIMESTAMP WITH TIMEZONE values in the 'PostgreSQL', 'SQL', and 'German' formats
correctly.
Note that you don't have to set this option if the PostgreSQL server has been set to use the
'ISO' format, which is the default.
• clone()
This method is provided for those who prefer to explicitly clone via a method called "clone()".
my $clone = $original->clone();
If called as a class method it will die.
METHODS
This class provides the following methods. The parse_datetime, parse_duration, format_datetime, and
format_duration methods are general-purpose methods provided for compatibility with other
"DateTime::Format" modules.
The other methods are specific to the corresponding PostgreSQL date/time data types. The names of these
methods are derived from the name of the PostgreSQL data type. (Note: Prior to PostgreSQL 7.3, the
TIMESTAMP type was equivalent to the TIMESTAMP WITH TIME ZONE type. This data type corresponds to the
format/parse_timestamp_with_time_zone method but not to the format/parse_timestamp method.)
PARSING METHODS
This class provides the following parsing methods.
As a general rule, the parsing methods accept input in any format that the PostgreSQL server can produce.
However, if PostgreSQL's DateStyle is set to 'SQL' or 'PostgreSQL', dates can only be parsed correctly if
the 'european' option is set correctly (i.e. same as the PostgreSQL server). The same is true for time
zones and the 'australian_timezones' option in all modes but 'ISO'.
The default DateStyle, 'ISO', will always produce unambiguous results and is also parsed most efficiently
by this parser class. I strongly recommend using this setting unless you have a good reason not to.
• parse_datetime($string,...)
Given a string containing a date and/or time representation, this method will return a new "DateTime"
object.
If the input string does not contain a date, it is set to 1970-01-01. If the input string does not
contain a time, it is set to 00:00:00. If the input string does not contain a time zone, it is set
to the floating time zone.
If given an improperly formatted string, this method may die.
• parse_timestamptz($string,...)
• parse_timestamp_with_time_zone($string,...)
Given a string containing a timestamp (date and time) representation, this method will return a new
"DateTime" object. This method is suitable for the TIMESTAMPTZ (or TIMESTAMP WITH TIME ZONE) type.
If the input string does not contain a time zone, it is set to the floating time zone.
Please note that PostgreSQL does not actually store a time zone along with the TIMESTAMP WITH TIME
ZONE (or TIMESTAMPTZ) type but will just return a time stamp converted for the server's local time
zone.
If given an improperly formatted string, this method may die.
• parse_timestamp($string,...)
• parse_timestamp_without_time_zone($string,...)
Similar to the functions above, but always returns a "DateTime" object with a floating time zone.
This method is suitable for the TIMESTAMP (or TIMESTAMP WITHOUT TIME ZONE) type.
If the server does return a time zone, it is ignored.
If given an improperly formatted string, this method may die.
• parse_timetz($string,...)
• parse_time_with_time_zone($string,...)
Given a string containing a time representation, this method will return a new "DateTime" object. The
date is set to 1970-01-01. This method is suitable for the TIMETZ (or TIME WITH TIME ZONE) type.
If the input string does not contain a time zone, it is set to the floating time zone.
Please note that PostgreSQL stores a numerical offset with its TIME WITH TIME ZONE (or TIMETZ) type.
It does not store a time zone name (such as 'Europe/Rome').
If given an improperly formatted string, this method may die.
• parse_time($string,...)
• parse_time_without_time_zone($string,...)
Similar to the functions above, but always returns an "DateTime" object with a floating time zone. If
the server returns a time zone, it is ignored. This method is suitable for use with the TIME (or TIME
WITHOUT TIME ZONE) type.
This ensures that the resulting "DateTime" object will always have the time zone expected by your
application.
If given an improperly formatted string, this method may die.
• parse_date($string,...)
Given a string containing a date representation, this method will return a new "DateTime" object. The
time is set to 00:00:00 (floating time zone). This method is suitable for the DATE type.
If given an improperly formatted string, this method may die.
• parse_duration($string)
• parse_interval($string)
Given a string containing a duration (SQL type INTERVAL) representation, this method will return a
new "DateTime::Duration" object.
If given an improperly formatted string, this method may die.
FORMATTING METHODS
This class provides the following formatting methods.
The output is always in the format mandated by the SQL standard (derived from ISO 8601), which is parsed
by PostgreSQL unambiguously in all DateStyle modes.
• format_datetime($datetime,...)
Given a "DateTime" object, this method returns a string appropriate as input for all date and
date/time types of PostgreSQL. It will contain date and time.
If the time zone of the "DateTime" part is floating, the resulting string will contain no time zone,
which will result in the server's time zone being used. Otherwise, the numerical offset of the time
zone is used.
• format_time($datetime,...)
• format_time_without_time_zone($datetime,...)
Given a "DateTime" object, this method returns a string appropriate as input for the TIME type (also
known as TIME WITHOUT TIME ZONE), which will contain the local time of the "DateTime" object and no
time zone.
• format_timetz($datetime)
• format_time_with_time_zone($datetime)
Given a "DateTime" object, this method returns a string appropriate as input for the TIME WITH TIME
ZONE type (also known as TIMETZ), which will contain the local part of the "DateTime" object and a
numerical time zone.
You should not use the TIME WITH TIME ZONE type to store dates with floating time zones. If the time
zone of the "DateTime" part is floating, the resulting string will contain no time zone, which will
result in the server's time zone being used.
• format_date($datetime)
Given a "DateTime" object, this method returns a string appropriate as input for the DATE type, which
will contain the date part of the "DateTime" object.
• format_timestamp($datetime)
• format_timestamp_without_time_zone($datetime)
Given a "DateTime" object, this method returns a string appropriate as input for the TIMESTAMP type
(also known as TIMESTAMP WITHOUT TIME ZONE), which will contain the local time of the "DateTime"
object and no time zone.
• format_timestamptz($datetime)
• format_timestamp_with_time_zone($datetime)
Given a "DateTime" object, this method returns a string appropriate as input for the TIMESTAMP WITH
TIME ZONE type, which will contain the local part of the "DateTime" object and a numerical time zone.
You should not use the TIMESTAMP WITH TIME ZONE type to store dates with floating time zones. If the
time zone of the "DateTime" part is floating, the resulting string will contain no time zone, which
will result in the server's time zone being used.
• format_duration($du)
• format_interval($du)
Given a "DateTime::Duration" object, this method returns a string appropriate as input for the
INTERVAL type.
LIMITATIONS
Some output formats of PostgreSQL have limitations that can only be passed on by this class.
As a general rules, none of these limitations apply to the 'ISO' output format. It is strongly
recommended to use this format (and to use PostgreSQL's to_char function when another output format
that's not supposed to be handled by a parser of this class is desired). 'ISO' is the default but you are
advised to explicitly set it at the beginning of the session by issuing a SET DATESTYLE TO 'ISO'; command
in case the server administrator changes that setting.
When formatting DateTime objects, this class always uses a format that's handled unambiguously by
PostgreSQL.
TIME ZONES
If DateStyle is set to 'PostgreSQL', 'SQL', or 'German', PostgreSQL does not send numerical time zones
for the TIMESTAMPTZ (or TIMESTAMP WITH TIME ZONE) type. Unfortunatly, the time zone names used instead
can be ambiguous: For example, 'EST' can mean -0500, +1000, or +1100.
You must set the 'server_tz' variable to a time zone that is identical to that of the PostgreSQL server.
If the server is set to a different time zone (or the underlying operating system interprets the time
zone differently), the parser will return wrong times.
You can avoid such problems by setting the server's time zone to UTC using the SET TIME ZONE 'UTC'
command and setting 'server_tz' parameter to 'UTC' (or by using the ISO output format, of course).
EUROPEAN DATES
For the SQL (for DATE and TIMSTAMP[TZ]) and the PostgreSQL (for DATE) output format, the server can send
dates in both European-style 'dd/mm/yyyy' and in US-style 'mm/dd/yyyy' format. In order to parse these
dates correctly, you have to pass the 'european' option to the constructor or to the "parse_xxx"
routines.
This problem does not occur when using the ISO or German output format (and for PostgreSQL with
TIMESTAMP[TZ] as month names are used then).
INTERVAL ELEMENTS
"DateTime::Duration" stores months, days, minutes and seconds separately. PostgreSQL only stores months
and seconds and disregards the irregular length of days due to DST switching and the irregular length of
minutes due to leap seconds. Therefore, it is not possible to store "DateTime::Duration" objects as SQL
INTERVALs without the loss of some information.
NEGATIVE INTERVALS
In the SQL and German output formats, the server does not send an indication of the sign with intervals.
This means that '1 month ago' and '1 month' are both returned as '1 mon'.
This problem can only be avoided by using the 'ISO' or 'PostgreSQL' output format.
SUPPORT
Support for this module is provided via the datetime@perl.org email list. See http://lists.perl.org/ for
more details.
AUTHOR
Daisuke Maki <daisuke@endeworks.jp>
AUTHOR EMERITUS
Claus A. Faerber <perl@faerber.muc.de>
COPYRIGHT
Copyright (c) 2003 Claus A. Faerber. Copyright (c) 2005-2007 Daisuke Maki
This program is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.
The full text of the license can be found in the LICENSE file included with this module.
SEE ALSO
datetime@perl.org mailing list
http://datetime.perl.org/