<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Date/Time Types</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 8.0.11 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Data Types" HREF="datatype.html"><LINK REL="PREVIOUS" TITLE="Binary Data Types" HREF="datatype-binary.html"><LINK REL="NEXT" TITLE="Boolean Type" HREF="datatype-boolean.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2007-02-02T03:57:22"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" >PostgreSQL 8.0.11 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="datatype-binary.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="datatype.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 8. Data Types</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="datatype.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="datatype-boolean.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="DATATYPE-DATETIME" >8.5. Date/Time Types</A ></H1 ><A NAME="AEN4192" ></A ><A NAME="AEN4194" ></A ><A NAME="AEN4196" ></A ><A NAME="AEN4198" ></A ><A NAME="AEN4200" ></A ><A NAME="AEN4202" ></A ><A NAME="AEN4204" ></A ><A NAME="AEN4206" ></A ><A NAME="AEN4208" ></A ><P > <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > supports the full set of <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > date and time types, shown in <A HREF="datatype-datetime.html#DATATYPE-DATETIME-TABLE" >Table 8-9</A >. The operations available on these data types are described in <A HREF="functions-datetime.html" >Section 9.9</A >. </P ><DIV CLASS="TABLE" ><A NAME="DATATYPE-DATETIME-TABLE" ></A ><P ><B >Table 8-9. Date/Time Types</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><COL><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Storage Size</TH ><TH >Description</TH ><TH >Low Value</TH ><TH >High Value</TH ><TH >Resolution</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="TYPE" >timestamp [ (<TT CLASS="REPLACEABLE" ><I >p</I ></TT >) ] [ without time zone ]</TT ></TD ><TD >8 bytes</TD ><TD >both date and time</TD ><TD >4713 BC</TD ><TD >5874897 AD</TD ><TD >1 microsecond / 14 digits</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >timestamp [ (<TT CLASS="REPLACEABLE" ><I >p</I ></TT >) ] with time zone</TT ></TD ><TD >8 bytes</TD ><TD >both date and time, with time zone</TD ><TD >4713 BC</TD ><TD >5874897 AD</TD ><TD >1 microsecond / 14 digits</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >interval [ (<TT CLASS="REPLACEABLE" ><I >p</I ></TT >) ]</TT ></TD ><TD >12 bytes</TD ><TD >time intervals</TD ><TD >-178000000 years</TD ><TD >178000000 years</TD ><TD >1 microsecond / 14 digits</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >date</TT ></TD ><TD >4 bytes</TD ><TD >dates only</TD ><TD >4713 BC</TD ><TD >5874897 AD</TD ><TD >1 day</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >time [ (<TT CLASS="REPLACEABLE" ><I >p</I ></TT >) ] [ without time zone ]</TT ></TD ><TD >8 bytes</TD ><TD >times of day only</TD ><TD >00:00:00.00</TD ><TD >23:59:59.99</TD ><TD >1 microsecond / 14 digits</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >time [ (<TT CLASS="REPLACEABLE" ><I >p</I ></TT >) ] with time zone</TT ></TD ><TD >12 bytes</TD ><TD >times of day only, with time zone</TD ><TD >00:00:00.00+12</TD ><TD >23:59:59.99-12</TD ><TD >1 microsecond / 14 digits</TD ></TR ></TBODY ></TABLE ></DIV ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > Prior to <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > 7.3, writing just <TT CLASS="TYPE" >timestamp</TT > was equivalent to <TT CLASS="TYPE" >timestamp with time zone</TT >. This was changed for SQL compliance. </P ></BLOCKQUOTE ></DIV ><P > <TT CLASS="TYPE" >time</TT >, <TT CLASS="TYPE" >timestamp</TT >, and <TT CLASS="TYPE" >interval</TT > accept an optional precision value <TT CLASS="REPLACEABLE" ><I >p</I ></TT > which specifies the number of fractional digits retained in the seconds field. By default, there is no explicit bound on precision. The allowed range of <TT CLASS="REPLACEABLE" ><I >p</I ></TT > is from 0 to 6 for the <TT CLASS="TYPE" >timestamp</TT > and <TT CLASS="TYPE" >interval</TT > types. </P ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > When <TT CLASS="TYPE" >timestamp</TT > values are stored as double precision floating-point numbers (currently the default), the effective limit of precision may be less than 6. <TT CLASS="TYPE" >timestamp</TT > values are stored as seconds before or after midnight 2000-01-01. Microsecond precision is achieved for dates within a few years of 2000-01-01, but the precision degrades for dates further away. When <TT CLASS="TYPE" >timestamp</TT > values are stored as eight-byte integers (a compile-time option), microsecond precision is available over the full range of values. However eight-byte integer timestamps have a more limited range of dates than shown above: from 4713 BC up to 294276 AD. The same compile-time option also determines whether <TT CLASS="TYPE" >time</TT > and <TT CLASS="TYPE" >interval</TT > values are stored as floating-point or eight-byte integers. In the floating-point case, large <TT CLASS="TYPE" >interval</TT > values degrade in precision as the size of the interval increases. </P ></BLOCKQUOTE ></DIV ><P > For the <TT CLASS="TYPE" >time</TT > types, the allowed range of <TT CLASS="REPLACEABLE" ><I >p</I ></TT > is from 0 to 6 when eight-byte integer storage is used, or from 0 to 10 when floating-point storage is used. </P ><P > The type <TT CLASS="TYPE" >time with time zone</TT > is defined by the SQL standard, but the definition exhibits properties which lead to questionable usefulness. In most cases, a combination of <TT CLASS="TYPE" >date</TT >, <TT CLASS="TYPE" >time</TT >, <TT CLASS="TYPE" >timestamp without time zone</TT >, and <TT CLASS="TYPE" >timestamp with time zone</TT > should provide a complete range of date/time functionality required by any application. </P ><P > The types <TT CLASS="TYPE" >abstime</TT > and <TT CLASS="TYPE" >reltime</TT > are lower precision types which are used internally. You are discouraged from using these types in new applications and are encouraged to move any old ones over when appropriate. Any or all of these internal types might disappear in a future release. </P ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="DATATYPE-DATETIME-INPUT" >8.5.1. Date/Time Input</A ></H2 ><P > Date and time input is accepted in almost any reasonable format, including ISO 8601, <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM >-compatible, traditional <SPAN CLASS="PRODUCTNAME" >POSTGRES</SPAN >, and others. For some formats, ordering of month, day, and year in date input is ambiguous and there is support for specifying the expected ordering of these fields. Set the <A HREF="runtime-config.html#GUC-DATESTYLE" >DateStyle</A > parameter to <TT CLASS="LITERAL" >MDY</TT > to select month-day-year interpretation, <TT CLASS="LITERAL" >DMY</TT > to select day-month-year interpretation, or <TT CLASS="LITERAL" >YMD</TT > to select year-month-day interpretation. </P ><P > <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > is more flexible in handling date/time input than the <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > standard requires. See <A HREF="datetime-appendix.html" >Appendix B</A > for the exact parsing rules of date/time input and for the recognized text fields including months, days of the week, and time zones. </P ><P > Remember that any date or time literal input needs to be enclosed in single quotes, like text strings. Refer to <A HREF="sql-syntax.html#SQL-SYNTAX-CONSTANTS-GENERIC" >Section 4.1.2.5</A > for more information. <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > requires the following syntax </P><PRE CLASS="SYNOPSIS" ><TT CLASS="REPLACEABLE" ><I >type</I ></TT > [ (<TT CLASS="REPLACEABLE" ><I >p</I ></TT >) ] '<TT CLASS="REPLACEABLE" ><I >value</I ></TT >'</PRE ><P> where <TT CLASS="REPLACEABLE" ><I >p</I ></TT > in the optional precision specification is an integer corresponding to the number of fractional digits in the seconds field. Precision can be specified for <TT CLASS="TYPE" >time</TT >, <TT CLASS="TYPE" >timestamp</TT >, and <TT CLASS="TYPE" >interval</TT > types. The allowed values are mentioned above. If no precision is specified in a constant specification, it defaults to the precision of the literal value. </P ><DIV CLASS="SECT3" ><H3 CLASS="SECT3" ><A NAME="AEN4337" >8.5.1.1. Dates</A ></H3 ><A NAME="AEN4339" ></A ><P > <A HREF="datatype-datetime.html#DATATYPE-DATETIME-DATE-TABLE" >Table 8-10</A > shows some possible inputs for the <TT CLASS="TYPE" >date</TT > type. </P ><DIV CLASS="TABLE" ><A NAME="DATATYPE-DATETIME-DATE-TABLE" ></A ><P ><B >Table 8-10. Date Input</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><THEAD ><TR ><TH >Example</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD >January 8, 1999</TD ><TD >unambiguous in any <TT CLASS="VARNAME" >datestyle</TT > input mode</TD ></TR ><TR ><TD >1999-01-08</TD ><TD >ISO 8601; January 8 in any mode (recommended format)</TD ></TR ><TR ><TD >1/8/1999</TD ><TD >January 8 in <TT CLASS="LITERAL" >MDY</TT > mode; August 1 in <TT CLASS="LITERAL" >DMY</TT > mode</TD ></TR ><TR ><TD >1/18/1999</TD ><TD >January 18 in <TT CLASS="LITERAL" >MDY</TT > mode; rejected in other modes</TD ></TR ><TR ><TD >01/02/03</TD ><TD >January 2, 2003 in <TT CLASS="LITERAL" >MDY</TT > mode; February 1, 2003 in <TT CLASS="LITERAL" >DMY</TT > mode; February 3, 2001 in <TT CLASS="LITERAL" >YMD</TT > mode </TD ></TR ><TR ><TD >1999-Jan-08</TD ><TD >January 8 in any mode</TD ></TR ><TR ><TD >Jan-08-1999</TD ><TD >January 8 in any mode</TD ></TR ><TR ><TD >08-Jan-1999</TD ><TD >January 8 in any mode</TD ></TR ><TR ><TD >99-Jan-08</TD ><TD >January 8 in <TT CLASS="LITERAL" >YMD</TT > mode, else error</TD ></TR ><TR ><TD >08-Jan-99</TD ><TD >January 8, except error in <TT CLASS="LITERAL" >YMD</TT > mode</TD ></TR ><TR ><TD >Jan-08-99</TD ><TD >January 8, except error in <TT CLASS="LITERAL" >YMD</TT > mode</TD ></TR ><TR ><TD >19990108</TD ><TD >ISO 8601; January 8, 1999 in any mode</TD ></TR ><TR ><TD >990108</TD ><TD >ISO 8601; January 8, 1999 in any mode</TD ></TR ><TR ><TD >1999.008</TD ><TD >year and day of year</TD ></TR ><TR ><TD >J2451187</TD ><TD >Julian day</TD ></TR ><TR ><TD >January 8, 99 BC</TD ><TD >year 99 before the Common Era</TD ></TR ></TBODY ></TABLE ></DIV ></DIV ><DIV CLASS="SECT3" ><H3 CLASS="SECT3" ><A NAME="AEN4410" >8.5.1.2. Times</A ></H3 ><A NAME="AEN4412" ></A ><A NAME="AEN4414" ></A ><A NAME="AEN4416" ></A ><P > The time-of-day types are <TT CLASS="TYPE" >time [ (<TT CLASS="REPLACEABLE" ><I >p</I ></TT >) ] without time zone</TT > and <TT CLASS="TYPE" >time [ (<TT CLASS="REPLACEABLE" ><I >p</I ></TT >) ] with time zone</TT >. Writing just <TT CLASS="TYPE" >time</TT > is equivalent to <TT CLASS="TYPE" >time without time zone</TT >. </P ><P > Valid input for these types consists of a time of day followed by an optional time zone. (See <A HREF="datatype-datetime.html#DATATYPE-DATETIME-TIME-TABLE" >Table 8-11</A > and <A HREF="datatype-datetime.html#DATATYPE-TIMEZONE-TABLE" >Table 8-12</A >.) If a time zone is specified in the input for <TT CLASS="TYPE" >time without time zone</TT >, it is silently ignored. </P ><DIV CLASS="TABLE" ><A NAME="DATATYPE-DATETIME-TIME-TABLE" ></A ><P ><B >Table 8-11. Time Input</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><THEAD ><TR ><TH >Example</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="LITERAL" >04:05:06.789</TT ></TD ><TD >ISO 8601</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >04:05:06</TT ></TD ><TD >ISO 8601</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >04:05</TT ></TD ><TD >ISO 8601</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >040506</TT ></TD ><TD >ISO 8601</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >04:05 AM</TT ></TD ><TD >same as 04:05; AM does not affect value</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >04:05 PM</TT ></TD ><TD >same as 16:05; input hour must be <= 12</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >04:05:06.789-8</TT ></TD ><TD >ISO 8601</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >04:05:06-08:00</TT ></TD ><TD >ISO 8601</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >04:05-08:00</TT ></TD ><TD >ISO 8601</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >040506-08</TT ></TD ><TD >ISO 8601</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >04:05:06 PST</TT ></TD ><TD >time zone specified by name</TD ></TR ></TBODY ></TABLE ></DIV ><DIV CLASS="TABLE" ><A NAME="DATATYPE-TIMEZONE-TABLE" ></A ><P ><B >Table 8-12. Time Zone Input</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><THEAD ><TR ><TH >Example</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="LITERAL" >PST</TT ></TD ><TD >Pacific Standard Time</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >-8:00</TT ></TD ><TD >ISO-8601 offset for PST</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >-800</TT ></TD ><TD >ISO-8601 offset for PST</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >-8</TT ></TD ><TD >ISO-8601 offset for PST</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >zulu</TT ></TD ><TD >Military abbreviation for UTC</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >z</TT ></TD ><TD >Short form of <TT CLASS="LITERAL" >zulu</TT ></TD ></TR ></TBODY ></TABLE ></DIV ><P > Refer to <A HREF="datetime-appendix.html" >Appendix B</A > for a list of time zone names that are recognized for input. </P ></DIV ><DIV CLASS="SECT3" ><H3 CLASS="SECT3" ><A NAME="AEN4516" >8.5.1.3. Time Stamps</A ></H3 ><A NAME="AEN4518" ></A ><A NAME="AEN4520" ></A ><A NAME="AEN4522" ></A ><P > Valid input for the time stamp types consists of a concatenation of a date and a time, followed by an optional time zone, followed by an optional <TT CLASS="LITERAL" >AD</TT > or <TT CLASS="LITERAL" >BC</TT >. (Alternatively, <TT CLASS="LITERAL" >AD</TT >/<TT CLASS="LITERAL" >BC</TT > can appear before the time zone, but this is not the preferred ordering.) Thus </P><PRE CLASS="PROGRAMLISTING" >1999-01-08 04:05:06</PRE ><P> and </P><PRE CLASS="PROGRAMLISTING" >1999-01-08 04:05:06 -8:00</PRE ><P> are valid values, which follow the <ACRONYM CLASS="ACRONYM" >ISO</ACRONYM > 8601 standard. In addition, the wide-spread format </P><PRE CLASS="PROGRAMLISTING" >January 8 04:05:06 1999 PST</PRE ><P> is supported. </P ><P > The <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > standard differentiates <TT CLASS="TYPE" >timestamp without time zone</TT > and <TT CLASS="TYPE" >timestamp with time zone</TT > literals by the existence of a <SPAN CLASS="QUOTE" >"+"</SPAN >; or <SPAN CLASS="QUOTE" >"-"</SPAN >. Hence, according to the standard, </P><PRE CLASS="PROGRAMLISTING" >TIMESTAMP '2004-10-19 10:23:54'</PRE ><P> is a <TT CLASS="TYPE" >timestamp without time zone</TT >, while </P><PRE CLASS="PROGRAMLISTING" >TIMESTAMP '2004-10-19 10:23:54+02'</PRE ><P> is a <TT CLASS="TYPE" >timestamp with time zone</TT >. <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > differs from the standard by requiring that <TT CLASS="TYPE" >timestamp with time zone</TT > literals be explicitly typed: </P><PRE CLASS="PROGRAMLISTING" >TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+02'</PRE ><P> If a literal is not explicitly indicated as being of <TT CLASS="TYPE" >timestamp with time zone</TT >, PostgreSQL will silently ignore any time zone indication in the literal. That is, the resulting date/time value is derived from the date/time fields in the input value, and is not adjusted for time zone. </P ><P > For <TT CLASS="TYPE" >timestamp with time zone</TT >, the internally stored value is always in UTC (Universal Coordinated Time, traditionally known as Greenwich Mean Time, <ACRONYM CLASS="ACRONYM" >GMT</ACRONYM >). An input value that has an explicit time zone specified is converted to UTC using the appropriate offset for that time zone. If no time zone is stated in the input string, then it is assumed to be in the time zone indicated by the system's <A HREF="runtime-config.html#GUC-TIMEZONE" >timezone</A > parameter, and is converted to UTC using the offset for the <TT CLASS="VARNAME" >timezone</TT > zone. </P ><P > When a <TT CLASS="TYPE" >timestamp with time zone</TT > value is output, it is always converted from UTC to the current <TT CLASS="VARNAME" >timezone</TT > zone, and displayed as local time in that zone. To see the time in another time zone, either change <TT CLASS="VARNAME" >timezone</TT > or use the <TT CLASS="LITERAL" >AT TIME ZONE</TT > construct (see <A HREF="functions-datetime.html#FUNCTIONS-DATETIME-ZONECONVERT" >Section 9.9.3</A >). </P ><P > Conversions between <TT CLASS="TYPE" >timestamp without time zone</TT > and <TT CLASS="TYPE" >timestamp with time zone</TT > normally assume that the <TT CLASS="TYPE" >timestamp without time zone</TT > value should be taken or given as <TT CLASS="VARNAME" >timezone</TT > local time. A different zone reference can be specified for the conversion using <TT CLASS="LITERAL" >AT TIME ZONE</TT >. </P ></DIV ><DIV CLASS="SECT3" ><H3 CLASS="SECT3" ><A NAME="AEN4564" >8.5.1.4. Intervals</A ></H3 ><A NAME="AEN4566" ></A ><P > <TT CLASS="TYPE" >interval</TT > values can be written with the following syntax: </P><PRE CLASS="PROGRAMLISTING" >[<SPAN CLASS="OPTIONAL" >@</SPAN >] <TT CLASS="REPLACEABLE" ><I >quantity</I ></TT > <TT CLASS="REPLACEABLE" ><I >unit</I ></TT > [<SPAN CLASS="OPTIONAL" ><TT CLASS="REPLACEABLE" ><I >quantity</I ></TT > <TT CLASS="REPLACEABLE" ><I >unit</I ></TT >...</SPAN >] [<SPAN CLASS="OPTIONAL" ><TT CLASS="REPLACEABLE" ><I >direction</I ></TT ></SPAN >]</PRE ><P> Where: <TT CLASS="REPLACEABLE" ><I >quantity</I ></TT > is a number (possibly signed); <TT CLASS="REPLACEABLE" ><I >unit</I ></TT > is <TT CLASS="LITERAL" >second</TT >, <TT CLASS="LITERAL" >minute</TT >, <TT CLASS="LITERAL" >hour</TT >, <TT CLASS="LITERAL" >day</TT >, <TT CLASS="LITERAL" >week</TT >, <TT CLASS="LITERAL" >month</TT >, <TT CLASS="LITERAL" >year</TT >, <TT CLASS="LITERAL" >decade</TT >, <TT CLASS="LITERAL" >century</TT >, <TT CLASS="LITERAL" >millennium</TT >, or abbreviations or plurals of these units; <TT CLASS="REPLACEABLE" ><I >direction</I ></TT > can be <TT CLASS="LITERAL" >ago</TT > or empty. The at sign (<TT CLASS="LITERAL" >@</TT >) is optional noise. The amounts of different units are implicitly added up with appropriate sign accounting. </P ><P > Quantities of days, hours, minutes, and seconds can be specified without explicit unit markings. For example, <TT CLASS="LITERAL" >'1 12:59:10'</TT > is read the same as <TT CLASS="LITERAL" >'1 day 12 hours 59 min 10 sec'</TT >. </P ><P > The optional precision <TT CLASS="REPLACEABLE" ><I >p</I ></TT > should be between 0 and 6, and defaults to the precision of the input literal. </P ></DIV ><DIV CLASS="SECT3" ><H3 CLASS="SECT3" ><A NAME="AEN4599" >8.5.1.5. Special Values</A ></H3 ><A NAME="AEN4601" ></A ><A NAME="AEN4604" ></A ><P > <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > supports several special date/time input values for convenience, as shown in <A HREF="datatype-datetime.html#DATATYPE-DATETIME-SPECIAL-TABLE" >Table 8-13</A >. The values <TT CLASS="LITERAL" >infinity</TT > and <TT CLASS="LITERAL" >-infinity</TT > 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, <TT CLASS="LITERAL" >now</TT > 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. </P ><DIV CLASS="TABLE" ><A NAME="DATATYPE-DATETIME-SPECIAL-TABLE" ></A ><P ><B >Table 8-13. Special Date/Time Inputs</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><THEAD ><TR ><TH >Input String</TH ><TH >Valid Types</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="LITERAL" >epoch</TT ></TD ><TD ><TT CLASS="TYPE" >date</TT >, <TT CLASS="TYPE" >timestamp</TT ></TD ><TD >1970-01-01 00:00:00+00 (Unix system time zero)</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >infinity</TT ></TD ><TD ><TT CLASS="TYPE" >timestamp</TT ></TD ><TD >later than all other time stamps</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >-infinity</TT ></TD ><TD ><TT CLASS="TYPE" >timestamp</TT ></TD ><TD >earlier than all other time stamps</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >now</TT ></TD ><TD ><TT CLASS="TYPE" >date</TT >, <TT CLASS="TYPE" >time</TT >, <TT CLASS="TYPE" >timestamp</TT ></TD ><TD >current transaction's start time</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >today</TT ></TD ><TD ><TT CLASS="TYPE" >date</TT >, <TT CLASS="TYPE" >timestamp</TT ></TD ><TD >midnight today</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >tomorrow</TT ></TD ><TD ><TT CLASS="TYPE" >date</TT >, <TT CLASS="TYPE" >timestamp</TT ></TD ><TD >midnight tomorrow</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >yesterday</TT ></TD ><TD ><TT CLASS="TYPE" >date</TT >, <TT CLASS="TYPE" >timestamp</TT ></TD ><TD >midnight yesterday</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >allballs</TT ></TD ><TD ><TT CLASS="TYPE" >time</TT ></TD ><TD >00:00:00.00 UTC</TD ></TR ></TBODY ></TABLE ></DIV ><P > The following <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM >-compatible functions can also be used to obtain the current time value for the corresponding data type: <TT CLASS="LITERAL" >CURRENT_DATE</TT >, <TT CLASS="LITERAL" >CURRENT_TIME</TT >, <TT CLASS="LITERAL" >CURRENT_TIMESTAMP</TT >, <TT CLASS="LITERAL" >LOCALTIME</TT >, <TT CLASS="LITERAL" >LOCALTIMESTAMP</TT >. The latter four accept an optional precision specification. (See <A HREF="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" >Section 9.9.4</A >.) Note however that these are SQL functions and are <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >not</I ></SPAN > recognized as data input strings. </P ></DIV ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="DATATYPE-DATETIME-OUTPUT" >8.5.2. Date/Time Output</A ></H2 ><A NAME="AEN4687" ></A ><A NAME="AEN4691" ></A ><P > The output format of the date/time types can be set to one of the four styles ISO 8601, <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > (Ingres), traditional POSTGRES, and German, using the command <TT CLASS="LITERAL" >SET datestyle</TT >. The default is the <ACRONYM CLASS="ACRONYM" >ISO</ACRONYM > format. (The <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > standard requires the use of the ISO 8601 format. The name of the <SPAN CLASS="QUOTE" >"SQL"</SPAN > output format is a historical accident.) <A HREF="datatype-datetime.html#DATATYPE-DATETIME-OUTPUT-TABLE" >Table 8-14</A > shows examples of each output style. The output of the <TT CLASS="TYPE" >date</TT > and <TT CLASS="TYPE" >time</TT > types is of course only the date or time part in accordance with the given examples. </P ><DIV CLASS="TABLE" ><A NAME="DATATYPE-DATETIME-OUTPUT-TABLE" ></A ><P ><B >Table 8-14. Date/Time Output Styles</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><THEAD ><TR ><TH >Style Specification</TH ><TH >Description</TH ><TH >Example</TH ></TR ></THEAD ><TBODY ><TR ><TD >ISO</TD ><TD >ISO 8601/SQL standard</TD ><TD >1997-12-17 07:37:16-08</TD ></TR ><TR ><TD >SQL</TD ><TD >traditional style</TD ><TD >12/17/1997 07:37:16.00 PST</TD ></TR ><TR ><TD >POSTGRES</TD ><TD >original style</TD ><TD >Wed Dec 17 07:37:16 1997 PST</TD ></TR ><TR ><TD >German</TD ><TD >regional style</TD ><TD >17.12.1997 07:37:16.00 PST</TD ></TR ></TBODY ></TABLE ></DIV ><P > In the <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > and POSTGRES styles, day appears before month if DMY field ordering has been specified, otherwise month appears before day. (See <A HREF="datatype-datetime.html#DATATYPE-DATETIME-INPUT" >Section 8.5.1</A > for how this setting also affects interpretation of input values.) <A HREF="datatype-datetime.html#DATATYPE-DATETIME-OUTPUT2-TABLE" >Table 8-15</A > shows an example. </P ><DIV CLASS="TABLE" ><A NAME="DATATYPE-DATETIME-OUTPUT2-TABLE" ></A ><P ><B >Table 8-15. Date Order Conventions</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><THEAD ><TR ><TH ><TT CLASS="VARNAME" >datestyle</TT > Setting</TH ><TH >Input Ordering</TH ><TH >Example Output</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="LITERAL" >SQL, DMY</TT ></TD ><TD ><TT CLASS="REPLACEABLE" ><I >day</I ></TT >/<TT CLASS="REPLACEABLE" ><I >month</I ></TT >/<TT CLASS="REPLACEABLE" ><I >year</I ></TT ></TD ><TD >17/12/1997 15:37:16.00 CET</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >SQL, MDY</TT ></TD ><TD ><TT CLASS="REPLACEABLE" ><I >month</I ></TT >/<TT CLASS="REPLACEABLE" ><I >day</I ></TT >/<TT CLASS="REPLACEABLE" ><I >year</I ></TT ></TD ><TD >12/17/1997 07:37:16.00 PST</TD ></TR ><TR ><TD ><TT CLASS="LITERAL" >Postgres, DMY</TT ></TD ><TD ><TT CLASS="REPLACEABLE" ><I >day</I ></TT >/<TT CLASS="REPLACEABLE" ><I >month</I ></TT >/<TT CLASS="REPLACEABLE" ><I >year</I ></TT ></TD ><TD >Wed 17 Dec 07:37:16 1997 PST</TD ></TR ></TBODY ></TABLE ></DIV ><P > <TT CLASS="TYPE" >interval</TT > output looks like the input format, except that units like <TT CLASS="LITERAL" >century</TT > or <TT CLASS="LITERAL" >week</TT > are converted to years and days and <TT CLASS="LITERAL" >ago</TT > is converted to an appropriate sign. In ISO mode the output looks like </P><PRE CLASS="PROGRAMLISTING" >[<SPAN CLASS="OPTIONAL" > <TT CLASS="REPLACEABLE" ><I >quantity</I ></TT > <TT CLASS="REPLACEABLE" ><I >unit</I ></TT > [<SPAN CLASS="OPTIONAL" > ... </SPAN >] </SPAN >] [<SPAN CLASS="OPTIONAL" > <TT CLASS="REPLACEABLE" ><I >days</I ></TT > </SPAN >] [<SPAN CLASS="OPTIONAL" > <TT CLASS="REPLACEABLE" ><I >hours</I ></TT >:<TT CLASS="REPLACEABLE" ><I >minutes</I ></TT >:<TT CLASS="REPLACEABLE" ><I >seconds</I ></TT > </SPAN >]</PRE ><P> </P ><P > The date/time styles can be selected by the user using the <TT CLASS="COMMAND" >SET datestyle</TT > command, the <A HREF="runtime-config.html#GUC-DATESTYLE" >DateStyle</A > parameter in the <TT CLASS="FILENAME" >postgresql.conf</TT > configuration file, or the <TT CLASS="ENVAR" >PGDATESTYLE</TT > environment variable on the server or client. The formatting function <CODE CLASS="FUNCTION" >to_char</CODE > (see <A HREF="functions-formatting.html" >Section 9.8</A >) is also available as a more flexible way to format the date/time output. </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="DATATYPE-TIMEZONES" >8.5.3. Time Zones</A ></H2 ><A NAME="AEN4792" ></A ><P > Time zones, and time-zone conventions, are influenced by political decisions, not just earth geometry. Time zones around the world became somewhat standardized during the 1900's, but continue to be prone to arbitrary changes, particularly with respect to daylight-savings rules. <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > currently supports daylight-savings rules over the time period 1902 through 2038 (corresponding to the full range of conventional Unix system time). Times outside that range are taken to be in <SPAN CLASS="QUOTE" >"standard time"</SPAN > for the selected time zone, no matter what part of the year they fall in. </P ><P > <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > endeavors to be compatible with the <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > standard definitions for typical usage. However, the <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > standard has an odd mix of date and time types and capabilities. Two obvious problems are: <P ></P ></P><UL ><LI ><P > Although the <TT CLASS="TYPE" >date</TT > type does not have an associated time zone, the <TT CLASS="TYPE" >time</TT > type can. Time zones in the real world have little meaning unless associated with a date as well as a time, since the offset may vary through the year with daylight-saving time boundaries. </P ></LI ><LI ><P > The default time zone is specified as a constant numeric offset from <ACRONYM CLASS="ACRONYM" >UTC</ACRONYM >. It is therefore not possible to adapt to daylight-saving time when doing date/time arithmetic across <ACRONYM CLASS="ACRONYM" >DST</ACRONYM > boundaries. </P ></LI ></UL ><P> </P ><P > To address these difficulties, we recommend using date/time types that contain both date and time when using time zones. We recommend <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >not</I ></SPAN > using the type <TT CLASS="TYPE" >time with time zone</TT > (though it is supported by <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > for legacy applications and for compliance with the <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > standard). <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > assumes your local time zone for any type containing only date or time. </P ><P > All timezone-aware dates and times are stored internally in <ACRONYM CLASS="ACRONYM" >UTC</ACRONYM >. They are converted to local time in the zone specified by the <A HREF="runtime-config.html#GUC-TIMEZONE" >timezone</A > configuration parameter before being displayed to the client. </P ><P > The <A HREF="runtime-config.html#GUC-TIMEZONE" >timezone</A > configuration parameter can be set in the file <TT CLASS="FILENAME" >postgresql.conf</TT >, or in any of the other standard ways described in <A HREF="runtime-config.html" >Section 16.4</A >. There are also several special ways to set it: <P ></P ></P><UL ><LI ><P > If <TT CLASS="VARNAME" >timezone</TT > is not specified in <TT CLASS="FILENAME" >postgresql.conf</TT > nor as a postmaster command-line switch, the server attempts to use the value of the <TT CLASS="ENVAR" >TZ</TT > environment variable as the default time zone. If <TT CLASS="ENVAR" >TZ</TT > is not defined or is not any of the time zone names known to <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN >, the server attempts to determine the operating system's default time zone by checking the behavior of the C library function <TT CLASS="LITERAL" >localtime()</TT >. The default time zone is selected as the closest match among <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN >'s known time zones. </P ></LI ><LI ><P > The <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > command <TT CLASS="COMMAND" >SET TIME ZONE</TT > sets the time zone for the session. This is an alternative spelling of <TT CLASS="COMMAND" >SET TIMEZONE TO</TT > with a more SQL-spec-compatible syntax. </P ></LI ><LI ><P > The <TT CLASS="ENVAR" >PGTZ</TT > environment variable, if set at the client, is used by <SPAN CLASS="APPLICATION" >libpq</SPAN > applications to send a <TT CLASS="COMMAND" >SET TIME ZONE</TT > command to the server upon connection. </P ></LI ></UL ><P> </P ><P > Refer to <A HREF="datetime-appendix.html" >Appendix B</A > for a list of available time zones. </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="DATATYPE-DATETIME-INTERNALS" >8.5.4. Internals</A ></H2 ><P > <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > uses Julian dates for all date/time calculations. They have the nice property of correctly predicting/calculating any date more recent than 4713 BC to far into the future, using the assumption that the length of the year is 365.2425 days. </P ><P > Date conventions before the 19th century make for interesting reading, but are not consistent enough to warrant coding into a date/time handler. </P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="datatype-binary.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="datatype-boolean.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Binary Data Types</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="datatype.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Boolean Type</TD ></TR ></TABLE ></DIV ></BODY ></HTML >