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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>9.9. Date/Time Functions and Operators</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="functions-formatting.html" title="9.8. Data Type Formatting Functions" /><link rel="next" href="functions-enum.html" title="9.10. Enum Support Functions" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.9. Date/Time Functions and Operators</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-formatting.html" title="9.8. Data Type Formatting Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><th width="60%" align="center">Chapter 9. Functions and Operators</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-enum.html" title="9.10. Enum Support Functions">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="FUNCTIONS-DATETIME"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.9. Date/Time Functions and Operators</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT">9.9.1. <code class="function">EXTRACT</code>, <code class="function">date_part</code></a></span></dt><dt><span class="sect2"><a href="functions-datetime.html#FUNCTIONS-DATETIME-TRUNC">9.9.2. <code class="function">date_trunc</code></a></span></dt><dt><span class="sect2"><a href="functions-datetime.html#FUNCTIONS-DATETIME-ZONECONVERT">9.9.3. <code class="literal">AT TIME ZONE</code></a></span></dt><dt><span class="sect2"><a href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT">9.9.4. Current Date/Time</a></span></dt><dt><span class="sect2"><a href="functions-datetime.html#FUNCTIONS-DATETIME-DELAY">9.9.5. Delaying Execution</a></span></dt></dl></div><p>
<a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-TABLE" title="Table 9.30. Date/Time Functions">Table 9.30</a> shows the available
functions for date/time value processing, with details appearing in
the following subsections. <a class="xref" href="functions-datetime.html#OPERATORS-DATETIME-TABLE" title="Table 9.29. Date/Time Operators">Table 9.29</a> illustrates the behaviors of
the basic arithmetic operators (<code class="literal">+</code>,
<code class="literal">*</code>, etc.). For formatting functions, refer to
<a class="xref" href="functions-formatting.html" title="9.8. Data Type Formatting Functions">Section 9.8</a>. You should be familiar with
the background information on date/time data types from <a class="xref" href="datatype-datetime.html" title="8.5. Date/Time Types">Section 8.5</a>.
</p><p>
All the functions and operators described below that take <code class="type">time</code> or <code class="type">timestamp</code>
inputs actually come in two variants: one that takes <code class="type">time with time zone</code> or <code class="type">timestamp
with time zone</code>, and one that takes <code class="type">time without time zone</code> or <code class="type">timestamp without time zone</code>.
For brevity, these variants are not shown separately. Also, the
<code class="literal">+</code> and <code class="literal">*</code> operators come in commutative pairs (for
example both date + integer and integer + date); we show only one of each
such pair.
</p><div class="table" id="OPERATORS-DATETIME-TABLE"><p class="title"><strong>Table 9.29. Date/Time Operators</strong></p><div class="table-contents"><table class="table" summary="Date/Time Operators" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Operator</th><th>Example</th><th>Result</th></tr></thead><tbody><tr><td> <code class="literal">+</code> </td><td><code class="literal">date '2001-09-28' + integer '7'</code></td><td><code class="literal">date '2001-10-05'</code></td></tr><tr><td> <code class="literal">+</code> </td><td><code class="literal">date '2001-09-28' + interval '1 hour'</code></td><td><code class="literal">timestamp '2001-09-28 01:00:00'</code></td></tr><tr><td> <code class="literal">+</code> </td><td><code class="literal">date '2001-09-28' + time '03:00'</code></td><td><code class="literal">timestamp '2001-09-28 03:00:00'</code></td></tr><tr><td> <code class="literal">+</code> </td><td><code class="literal">interval '1 day' + interval '1 hour'</code></td><td><code class="literal">interval '1 day 01:00:00'</code></td></tr><tr><td> <code class="literal">+</code> </td><td><code class="literal">timestamp '2001-09-28 01:00' + interval '23 hours'</code></td><td><code class="literal">timestamp '2001-09-29 00:00:00'</code></td></tr><tr><td> <code class="literal">+</code> </td><td><code class="literal">time '01:00' + interval '3 hours'</code></td><td><code class="literal">time '04:00:00'</code></td></tr><tr><td> <code class="literal">-</code> </td><td><code class="literal">- interval '23 hours'</code></td><td><code class="literal">interval '-23:00:00'</code></td></tr><tr><td> <code class="literal">-</code> </td><td><code class="literal">date '2001-10-01' - date '2001-09-28'</code></td><td><code class="literal">integer '3'</code> (days)</td></tr><tr><td> <code class="literal">-</code> </td><td><code class="literal">date '2001-10-01' - integer '7'</code></td><td><code class="literal">date '2001-09-24'</code></td></tr><tr><td> <code class="literal">-</code> </td><td><code class="literal">date '2001-09-28' - interval '1 hour'</code></td><td><code class="literal">timestamp '2001-09-27 23:00:00'</code></td></tr><tr><td> <code class="literal">-</code> </td><td><code class="literal">time '05:00' - time '03:00'</code></td><td><code class="literal">interval '02:00:00'</code></td></tr><tr><td> <code class="literal">-</code> </td><td><code class="literal">time '05:00' - interval '2 hours'</code></td><td><code class="literal">time '03:00:00'</code></td></tr><tr><td> <code class="literal">-</code> </td><td><code class="literal">timestamp '2001-09-28 23:00' - interval '23 hours'</code></td><td><code class="literal">timestamp '2001-09-28 00:00:00'</code></td></tr><tr><td> <code class="literal">-</code> </td><td><code class="literal">interval '1 day' - interval '1 hour'</code></td><td><code class="literal">interval '1 day -01:00:00'</code></td></tr><tr><td> <code class="literal">-</code> </td><td><code class="literal">timestamp '2001-09-29 03:00' - timestamp '2001-09-27 12:00'</code></td><td><code class="literal">interval '1 day 15:00:00'</code></td></tr><tr><td> <code class="literal">*</code> </td><td><code class="literal">900 * interval '1 second'</code></td><td><code class="literal">interval '00:15:00'</code></td></tr><tr><td> <code class="literal">*</code> </td><td><code class="literal">21 * interval '1 day'</code></td><td><code class="literal">interval '21 days'</code></td></tr><tr><td> <code class="literal">*</code> </td><td><code class="literal">double precision '3.5' * interval '1 hour'</code></td><td><code class="literal">interval '03:30:00'</code></td></tr><tr><td> <code class="literal">/</code> </td><td><code class="literal">interval '1 hour' / double precision '1.5'</code></td><td><code class="literal">interval '00:40:00'</code></td></tr></tbody></table></div></div><br class="table-break" /><div class="table" id="FUNCTIONS-DATETIME-TABLE"><p class="title"><strong>Table 9.30. Date/Time Functions</strong></p><div class="table-contents"><table class="table" summary="Date/Time Functions" border="1"><colgroup><col /><col /><col /><col /><col /></colgroup><thead><tr><th>Function</th><th>Return Type</th><th>Description</th><th>Example</th><th>Result</th></tr></thead><tbody><tr><td>
<a id="id-1.5.8.14.5.2.2.1.1.1" class="indexterm"></a>
<code class="literal"><code class="function">age(<code class="type">timestamp</code>, <code class="type">timestamp</code>)</code></code>
</td><td><code class="type">interval</code></td><td>Subtract arguments, producing a <span class="quote">“<span class="quote">symbolic</span>”</span> result that
uses years and months, rather than just days</td><td><code class="literal">age(timestamp '2001-04-10', timestamp '1957-06-13')</code></td><td><code class="literal">43 years 9 mons 27 days</code></td></tr><tr><td><code class="literal"><code class="function">age(<code class="type">timestamp</code>)</code></code></td><td><code class="type">interval</code></td><td>Subtract from <code class="function">current_date</code> (at midnight)</td><td><code class="literal">age(timestamp '1957-06-13')</code></td><td><code class="literal">43 years 8 mons 3 days</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.3.1.1" class="indexterm"></a>
<code class="literal"><code class="function">clock_timestamp()</code></code>
</td><td><code class="type">timestamp with time zone</code></td><td>Current date and time (changes during statement execution);
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" title="9.9.4. Current Date/Time">Section 9.9.4</a>
</td><td> </td><td> </td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.4.1.1" class="indexterm"></a>
<code class="literal"><code class="function">current_date</code></code>
</td><td><code class="type">date</code></td><td>Current date;
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" title="9.9.4. Current Date/Time">Section 9.9.4</a>
</td><td> </td><td> </td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.5.1.1" class="indexterm"></a>
<code class="literal"><code class="function">current_time</code></code>
</td><td><code class="type">time with time zone</code></td><td>Current time of day;
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" title="9.9.4. Current Date/Time">Section 9.9.4</a>
</td><td> </td><td> </td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.6.1.1" class="indexterm"></a>
<code class="literal"><code class="function">current_timestamp</code></code>
</td><td><code class="type">timestamp with time zone</code></td><td>Current date and time (start of current transaction);
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" title="9.9.4. Current Date/Time">Section 9.9.4</a>
</td><td> </td><td> </td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.7.1.1" class="indexterm"></a>
<code class="literal"><code class="function">date_part(<code class="type">text</code>, <code class="type">timestamp</code>)</code></code>
</td><td><code class="type">double precision</code></td><td>Get subfield (equivalent to <code class="function">extract</code>);
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT" title="9.9.1. EXTRACT, date_part">Section 9.9.1</a>
</td><td><code class="literal">date_part('hour', timestamp '2001-02-16 20:38:40')</code></td><td><code class="literal">20</code></td></tr><tr><td><code class="literal"><code class="function">date_part(<code class="type">text</code>, <code class="type">interval</code>)</code></code></td><td><code class="type">double precision</code></td><td>Get subfield (equivalent to
<code class="function">extract</code>); see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT" title="9.9.1. EXTRACT, date_part">Section 9.9.1</a>
</td><td><code class="literal">date_part('month', interval '2 years 3 months')</code></td><td><code class="literal">3</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.9.1.1" class="indexterm"></a>
<code class="literal"><code class="function">date_trunc(<code class="type">text</code>, <code class="type">timestamp</code>)</code></code>
</td><td><code class="type">timestamp</code></td><td>Truncate to specified precision; see also <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-TRUNC" title="9.9.2. date_trunc">Section 9.9.2</a>
</td><td><code class="literal">date_trunc('hour', timestamp '2001-02-16 20:38:40')</code></td><td><code class="literal">2001-02-16 20:00:00</code></td></tr><tr><td><code class="literal"><code class="function">date_trunc(<code class="type">text</code>, <code class="type">interval</code>)</code></code></td><td><code class="type">interval</code></td><td>Truncate to specified precision; see also <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-TRUNC" title="9.9.2. date_trunc">Section 9.9.2</a>
</td><td><code class="literal">date_trunc('hour', interval '2 days 3 hours 40 minutes')</code></td><td><code class="literal">2 days 03:00:00</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.11.1.1" class="indexterm"></a>
<code class="literal"><code class="function">extract</code>(<em class="parameter"><code>field</code></em> from
<code class="type">timestamp</code>)</code>
</td><td><code class="type">double precision</code></td><td>Get subfield; see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT" title="9.9.1. EXTRACT, date_part">Section 9.9.1</a>
</td><td><code class="literal">extract(hour from timestamp '2001-02-16 20:38:40')</code></td><td><code class="literal">20</code></td></tr><tr><td><code class="literal"><code class="function">extract</code>(<em class="parameter"><code>field</code></em> from
<code class="type">interval</code>)</code></td><td><code class="type">double precision</code></td><td>Get subfield; see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT" title="9.9.1. EXTRACT, date_part">Section 9.9.1</a>
</td><td><code class="literal">extract(month from interval '2 years 3 months')</code></td><td><code class="literal">3</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.13.1.1" class="indexterm"></a>
<code class="literal"><code class="function">isfinite(<code class="type">date</code>)</code></code>
</td><td><code class="type">boolean</code></td><td>Test for finite date (not +/-infinity)</td><td><code class="literal">isfinite(date '2001-02-16')</code></td><td><code class="literal">true</code></td></tr><tr><td><code class="literal"><code class="function">isfinite(<code class="type">timestamp</code>)</code></code></td><td><code class="type">boolean</code></td><td>Test for finite time stamp (not +/-infinity)</td><td><code class="literal">isfinite(timestamp '2001-02-16 21:28:30')</code></td><td><code class="literal">true</code></td></tr><tr><td><code class="literal"><code class="function">isfinite(<code class="type">interval</code>)</code></code></td><td><code class="type">boolean</code></td><td>Test for finite interval</td><td><code class="literal">isfinite(interval '4 hours')</code></td><td><code class="literal">true</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.16.1.1" class="indexterm"></a>
<code class="literal"><code class="function">justify_days(<code class="type">interval</code>)</code></code>
</td><td><code class="type">interval</code></td><td>Adjust interval so 30-day time periods are represented as months</td><td><code class="literal">justify_days(interval '35 days')</code></td><td><code class="literal">1 mon 5 days</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.17.1.1" class="indexterm"></a>
<code class="literal"><code class="function">justify_hours(<code class="type">interval</code>)</code></code>
</td><td><code class="type">interval</code></td><td>Adjust interval so 24-hour time periods are represented as days</td><td><code class="literal">justify_hours(interval '27 hours')</code></td><td><code class="literal">1 day 03:00:00</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.18.1.1" class="indexterm"></a>
<code class="literal"><code class="function">justify_interval(<code class="type">interval</code>)</code></code>
</td><td><code class="type">interval</code></td><td>Adjust interval using <code class="function">justify_days</code> and <code class="function">justify_hours</code>, with additional sign adjustments</td><td><code class="literal">justify_interval(interval '1 mon -1 hour')</code></td><td><code class="literal">29 days 23:00:00</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.19.1.1" class="indexterm"></a>
<code class="literal"><code class="function">localtime</code></code>
</td><td><code class="type">time</code></td><td>Current time of day;
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" title="9.9.4. Current Date/Time">Section 9.9.4</a>
</td><td> </td><td> </td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.20.1.1" class="indexterm"></a>
<code class="literal"><code class="function">localtimestamp</code></code>
</td><td><code class="type">timestamp</code></td><td>Current date and time (start of current transaction);
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" title="9.9.4. Current Date/Time">Section 9.9.4</a>
</td><td> </td><td> </td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.21.1.1" class="indexterm"></a>
<code class="literal">
<code class="function">
make_date(<em class="parameter"><code>year</code></em> <code class="type">int</code>,
<em class="parameter"><code>month</code></em> <code class="type">int</code>,
<em class="parameter"><code>day</code></em> <code class="type">int</code>)
</code>
</code>
</td><td><code class="type">date</code></td><td>
Create date from year, month and day fields
</td><td><code class="literal">make_date(2013, 7, 15)</code></td><td><code class="literal">2013-07-15</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.22.1.1" class="indexterm"></a>
<code class="literal">
<code class="function">
make_interval(<em class="parameter"><code>years</code></em> <code class="type">int</code> DEFAULT 0,
<em class="parameter"><code>months</code></em> <code class="type">int</code> DEFAULT 0,
<em class="parameter"><code>weeks</code></em> <code class="type">int</code> DEFAULT 0,
<em class="parameter"><code>days</code></em> <code class="type">int</code> DEFAULT 0,
<em class="parameter"><code>hours</code></em> <code class="type">int</code> DEFAULT 0,
<em class="parameter"><code>mins</code></em> <code class="type">int</code> DEFAULT 0,
<em class="parameter"><code>secs</code></em> <code class="type">double precision</code> DEFAULT 0.0)
</code>
</code>
</td><td><code class="type">interval</code></td><td>
Create interval from years, months, weeks, days, hours, minutes and
seconds fields
</td><td><code class="literal">make_interval(days => 10)</code></td><td><code class="literal">10 days</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.23.1.1" class="indexterm"></a>
<code class="literal">
<code class="function">
make_time(<em class="parameter"><code>hour</code></em> <code class="type">int</code>,
<em class="parameter"><code>min</code></em> <code class="type">int</code>,
<em class="parameter"><code>sec</code></em> <code class="type">double precision</code>)
</code>
</code>
</td><td><code class="type">time</code></td><td>
Create time from hour, minute and seconds fields
</td><td><code class="literal">make_time(8, 15, 23.5)</code></td><td><code class="literal">08:15:23.5</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.24.1.1" class="indexterm"></a>
<code class="literal">
<code class="function">
make_timestamp(<em class="parameter"><code>year</code></em> <code class="type">int</code>,
<em class="parameter"><code>month</code></em> <code class="type">int</code>,
<em class="parameter"><code>day</code></em> <code class="type">int</code>,
<em class="parameter"><code>hour</code></em> <code class="type">int</code>,
<em class="parameter"><code>min</code></em> <code class="type">int</code>,
<em class="parameter"><code>sec</code></em> <code class="type">double precision</code>)
</code>
</code>
</td><td><code class="type">timestamp</code></td><td>
Create timestamp from year, month, day, hour, minute and seconds fields
</td><td><code class="literal">make_timestamp(2013, 7, 15, 8, 15, 23.5)</code></td><td><code class="literal">2013-07-15 08:15:23.5</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.25.1.1" class="indexterm"></a>
<code class="literal">
<code class="function">
make_timestamptz(<em class="parameter"><code>year</code></em> <code class="type">int</code>,
<em class="parameter"><code>month</code></em> <code class="type">int</code>,
<em class="parameter"><code>day</code></em> <code class="type">int</code>,
<em class="parameter"><code>hour</code></em> <code class="type">int</code>,
<em class="parameter"><code>min</code></em> <code class="type">int</code>,
<em class="parameter"><code>sec</code></em> <code class="type">double precision</code>,
[<span class="optional"> <em class="parameter"><code>timezone</code></em> <code class="type">text</code> </span>])
</code>
</code>
</td><td><code class="type">timestamp with time zone</code></td><td>
Create timestamp with time zone from year, month, day, hour, minute
and seconds fields; if <em class="parameter"><code>timezone</code></em> is not
specified, the current time zone is used
</td><td><code class="literal">make_timestamptz(2013, 7, 15, 8, 15, 23.5)</code></td><td><code class="literal">2013-07-15 08:15:23.5+01</code></td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.26.1.1" class="indexterm"></a>
<code class="literal"><code class="function">now()</code></code>
</td><td><code class="type">timestamp with time zone</code></td><td>Current date and time (start of current transaction);
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" title="9.9.4. Current Date/Time">Section 9.9.4</a>
</td><td> </td><td> </td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.27.1.1" class="indexterm"></a>
<code class="literal"><code class="function">statement_timestamp()</code></code>
</td><td><code class="type">timestamp with time zone</code></td><td>Current date and time (start of current statement);
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" title="9.9.4. Current Date/Time">Section 9.9.4</a>
</td><td> </td><td> </td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.28.1.1" class="indexterm"></a>
<code class="literal"><code class="function">timeofday()</code></code>
</td><td><code class="type">text</code></td><td>Current date and time
(like <code class="function">clock_timestamp</code>, but as a <code class="type">text</code> string);
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" title="9.9.4. Current Date/Time">Section 9.9.4</a>
</td><td> </td><td> </td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.29.1.1" class="indexterm"></a>
<code class="literal"><code class="function">transaction_timestamp()</code></code>
</td><td><code class="type">timestamp with time zone</code></td><td>Current date and time (start of current transaction);
see <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT" title="9.9.4. Current Date/Time">Section 9.9.4</a>
</td><td> </td><td> </td></tr><tr><td>
<a id="id-1.5.8.14.5.2.2.30.1.1" class="indexterm"></a>
<code class="literal"><code class="function">to_timestamp(<code class="type">double precision</code>)</code></code>
</td><td><code class="type">timestamp with time zone</code></td><td>Convert Unix epoch (seconds since 1970-01-01 00:00:00+00) to
timestamp</td><td><code class="literal">to_timestamp(1284352323)</code></td><td><code class="literal">2010-09-13 04:32:03+00</code></td></tr></tbody></table></div></div><br class="table-break" /><p>
<a id="id-1.5.8.14.6.1" class="indexterm"></a>
In addition to these functions, the SQL <code class="literal">OVERLAPS</code> operator is
supported:
</p><pre class="synopsis">
(<em class="replaceable"><code>start1</code></em>, <em class="replaceable"><code>end1</code></em>) OVERLAPS (<em class="replaceable"><code>start2</code></em>, <em class="replaceable"><code>end2</code></em>)
(<em class="replaceable"><code>start1</code></em>, <em class="replaceable"><code>length1</code></em>) OVERLAPS (<em class="replaceable"><code>start2</code></em>, <em class="replaceable"><code>length2</code></em>)
</pre><p>
This expression yields true when two time periods (defined by their
endpoints) overlap, false when they do not overlap. The endpoints
can be specified as pairs of dates, times, or time stamps; or as
a date, time, or time stamp followed by an interval. When a pair
of values is provided, either the start or the end can be written
first; <code class="literal">OVERLAPS</code> automatically takes the earlier value
of the pair as the start. Each time period is considered to
represent the half-open interval <em class="replaceable"><code>start</code></em> <code class="literal"><=</code>
<em class="replaceable"><code>time</code></em> <code class="literal"><</code> <em class="replaceable"><code>end</code></em>, unless
<em class="replaceable"><code>start</code></em> and <em class="replaceable"><code>end</code></em> are equal in which case it
represents that single time instant. This means for instance that two
time periods with only an endpoint in common do not overlap.
</p><pre class="screen">
SELECT (DATE '2001-02-16', DATE '2001-12-21') OVERLAPS
(DATE '2001-10-30', DATE '2002-10-30');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">true</code>
SELECT (DATE '2001-02-16', INTERVAL '100 days') OVERLAPS
(DATE '2001-10-30', DATE '2002-10-30');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">false</code>
SELECT (DATE '2001-10-29', DATE '2001-10-30') OVERLAPS
(DATE '2001-10-30', DATE '2001-10-31');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">false</code>
SELECT (DATE '2001-10-30', DATE '2001-10-30') OVERLAPS
(DATE '2001-10-30', DATE '2001-10-31');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">true</code>
</pre><p>
When adding an <code class="type">interval</code> value to (or subtracting an
<code class="type">interval</code> value from) a <code class="type">timestamp with time zone</code>
value, the days component advances or decrements the date of the
<code class="type">timestamp with time zone</code> by the indicated number of days.
Across daylight saving time changes (when the session time zone is set to a
time zone that recognizes DST), this means <code class="literal">interval '1 day'</code>
does not necessarily equal <code class="literal">interval '24 hours'</code>.
For example, with the session time zone set to <code class="literal">CST7CDT</code>,
<code class="literal">timestamp with time zone '2005-04-02 12:00-07' + interval '1 day'</code>
will produce <code class="literal">timestamp with time zone '2005-04-03 12:00-06'</code>,
while adding <code class="literal">interval '24 hours'</code> to the same initial
<code class="type">timestamp with time zone</code> produces
<code class="literal">timestamp with time zone '2005-04-03 13:00-06'</code>, as there is
a change in daylight saving time at <code class="literal">2005-04-03 02:00</code> in time zone
<code class="literal">CST7CDT</code>.
</p><p>
Note there can be ambiguity in the <code class="literal">months</code> field returned by
<code class="function">age</code> because different months have different numbers of
days. <span class="productname">PostgreSQL</span>'s approach uses the month from the
earlier of the two dates when calculating partial months. For example,
<code class="literal">age('2004-06-01', '2004-04-30')</code> uses April to yield
<code class="literal">1 mon 1 day</code>, while using May would yield <code class="literal">1 mon 2
days</code> because May has 31 days, while April has only 30.
</p><p>
Subtraction of dates and timestamps can also be complex. One conceptually
simple way to perform subtraction is to convert each value to a number
of seconds using <code class="literal">EXTRACT(EPOCH FROM ...)</code>, then subtract the
results; this produces the
number of <span class="emphasis"><em>seconds</em></span> between the two values. This will adjust
for the number of days in each month, timezone changes, and daylight
saving time adjustments. Subtraction of date or timestamp
values with the <span class="quote">“<span class="quote"><code class="literal">-</code></span>”</span> operator
returns the number of days (24-hours) and hours/minutes/seconds
between the values, making the same adjustments. The <code class="function">age</code>
function returns years, months, days, and hours/minutes/seconds,
performing field-by-field subtraction and then adjusting for negative
field values. The following queries illustrate the differences in these
approaches. The sample results were produced with <code class="literal">timezone
= 'US/Eastern'</code>; there is a daylight saving time change between the
two dates used:
</p><pre class="screen">
SELECT EXTRACT(EPOCH FROM timestamptz '2013-07-01 12:00:00') -
EXTRACT(EPOCH FROM timestamptz '2013-03-01 12:00:00');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">10537200</code>
SELECT (EXTRACT(EPOCH FROM timestamptz '2013-07-01 12:00:00') -
EXTRACT(EPOCH FROM timestamptz '2013-03-01 12:00:00'))
/ 60 / 60 / 24;
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">121.958333333333</code>
SELECT timestamptz '2013-07-01 12:00:00' - timestamptz '2013-03-01 12:00:00';
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">121 days 23:00:00</code>
SELECT age(timestamptz '2013-07-01 12:00:00', timestamptz '2013-03-01 12:00:00');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">4 mons</code>
</pre><div class="sect2" id="FUNCTIONS-DATETIME-EXTRACT"><div class="titlepage"><div><div><h3 class="title">9.9.1. <code class="function">EXTRACT</code>, <code class="function">date_part</code></h3></div></div></div><a id="id-1.5.8.14.12.2" class="indexterm"></a><a id="id-1.5.8.14.12.3" class="indexterm"></a><pre class="synopsis">
EXTRACT(<em class="replaceable"><code>field</code></em> FROM <em class="replaceable"><code>source</code></em>)
</pre><p>
The <code class="function">extract</code> function retrieves subfields
such as year or hour from date/time values.
<em class="replaceable"><code>source</code></em> must be a value expression of
type <code class="type">timestamp</code>, <code class="type">time</code>, or <code class="type">interval</code>.
(Expressions of type <code class="type">date</code> are
cast to <code class="type">timestamp</code> and can therefore be used as
well.) <em class="replaceable"><code>field</code></em> is an identifier or
string that selects what field to extract from the source value.
The <code class="function">extract</code> function returns values of type
<code class="type">double precision</code>.
The following are valid field names:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">century</code></span></dt><dd><p>
The century
</p><pre class="screen">
SELECT EXTRACT(CENTURY FROM TIMESTAMP '2000-12-16 12:21:13');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">20</code>
SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">21</code>
</pre><p>
The first century starts at 0001-01-01 00:00:00 AD, although
they did not know it at the time. This definition applies to all
Gregorian calendar countries. There is no century number 0,
you go from -1 century to 1 century.
If you disagree with this, please write your complaint to:
Pope, Cathedral Saint-Peter of Roma, Vatican.
</p></dd><dt><span class="term"><code class="literal">day</code></span></dt><dd><p>
For <code class="type">timestamp</code> values, the day (of the month) field
(1 - 31) ; for <code class="type">interval</code> values, the number of days
</p><pre class="screen">
SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">16</code>
SELECT EXTRACT(DAY FROM INTERVAL '40 days 1 minute');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">40</code>
</pre></dd><dt><span class="term"><code class="literal">decade</code></span></dt><dd><p>
The year field divided by 10
</p><pre class="screen">
SELECT EXTRACT(DECADE FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">200</code>
</pre></dd><dt><span class="term"><code class="literal">dow</code></span></dt><dd><p>
The day of the week as Sunday (<code class="literal">0</code>) to
Saturday (<code class="literal">6</code>)
</p><pre class="screen">
SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">5</code>
</pre><p>
Note that <code class="function">extract</code>'s day of the week numbering
differs from that of the <code class="function">to_char(...,
'D')</code> function.
</p></dd><dt><span class="term"><code class="literal">doy</code></span></dt><dd><p>
The day of the year (1 - 365/366)
</p><pre class="screen">
SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">47</code>
</pre></dd><dt><span class="term"><code class="literal">epoch</code></span></dt><dd><p>
For <code class="type">timestamp with time zone</code> values, the
number of seconds since 1970-01-01 00:00:00 UTC (can be negative);
for <code class="type">date</code> and <code class="type">timestamp</code> values, the
number of seconds since 1970-01-01 00:00:00 local time;
for <code class="type">interval</code> values, the total number
of seconds in the interval
</p><pre class="screen">
SELECT EXTRACT(EPOCH FROM TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40.12-08');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">982384720.12</code>
SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">442800</code>
</pre><p>
You can convert an epoch value back to a time stamp
with <code class="function">to_timestamp</code>:
</p><pre class="screen">
SELECT to_timestamp(982384720.12);
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001-02-17 04:38:40.12+00</code>
</pre></dd><dt><span class="term"><code class="literal">hour</code></span></dt><dd><p>
The hour field (0 - 23)
</p><pre class="screen">
SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">20</code>
</pre></dd><dt><span class="term"><code class="literal">isodow</code></span></dt><dd><p>
The day of the week as Monday (<code class="literal">1</code>) to
Sunday (<code class="literal">7</code>)
</p><pre class="screen">
SELECT EXTRACT(ISODOW FROM TIMESTAMP '2001-02-18 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">7</code>
</pre><p>
This is identical to <code class="literal">dow</code> except for Sunday. This
matches the <acronym class="acronym">ISO</acronym> 8601 day of the week numbering.
</p></dd><dt><span class="term"><code class="literal">isoyear</code></span></dt><dd><p>
The <acronym class="acronym">ISO</acronym> 8601 week-numbering year that the date
falls in (not applicable to intervals)
</p><pre class="screen">
SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-01');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2005</code>
SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-02');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2006</code>
</pre><p>
Each <acronym class="acronym">ISO</acronym> 8601 week-numbering year begins with the
Monday of the week containing the 4th of January, so in early
January or late December the <acronym class="acronym">ISO</acronym> year may be
different from the Gregorian year. See the <code class="literal">week</code>
field for more information.
</p><p>
This field is not available in PostgreSQL releases prior to 8.3.
</p></dd><dt><span class="term"><code class="literal">microseconds</code></span></dt><dd><p>
The seconds field, including fractional parts, multiplied by 1
000 000; note that this includes full seconds
</p><pre class="screen">
SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">28500000</code>
</pre></dd><dt><span class="term"><code class="literal">millennium</code></span></dt><dd><p>
The millennium
</p><pre class="screen">
SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">3</code>
</pre><p>
Years in the 1900s are in the second millennium.
The third millennium started January 1, 2001.
</p></dd><dt><span class="term"><code class="literal">milliseconds</code></span></dt><dd><p>
The seconds field, including fractional parts, multiplied by
1000. Note that this includes full seconds.
</p><pre class="screen">
SELECT EXTRACT(MILLISECONDS FROM TIME '17:12:28.5');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">28500</code>
</pre></dd><dt><span class="term"><code class="literal">minute</code></span></dt><dd><p>
The minutes field (0 - 59)
</p><pre class="screen">
SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">38</code>
</pre></dd><dt><span class="term"><code class="literal">month</code></span></dt><dd><p>
For <code class="type">timestamp</code> values, the number of the month
within the year (1 - 12) ; for <code class="type">interval</code> values,
the number of months, modulo 12 (0 - 11)
</p><pre class="screen">
SELECT EXTRACT(MONTH FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2</code>
SELECT EXTRACT(MONTH FROM INTERVAL '2 years 3 months');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">3</code>
SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">1</code>
</pre></dd><dt><span class="term"><code class="literal">quarter</code></span></dt><dd><p>
The quarter of the year (1 - 4) that the date is in
</p><pre class="screen">
SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">1</code>
</pre></dd><dt><span class="term"><code class="literal">second</code></span></dt><dd><p>
The seconds field, including fractional parts (0 -
59<a href="#ftn.id-1.5.8.14.12.5.11.16.2.1.1" class="footnote"><sup class="footnote" id="id-1.5.8.14.12.5.11.16.2.1.1">[7]</sup></a>)
</p><pre class="screen">
SELECT EXTRACT(SECOND FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">40</code>
SELECT EXTRACT(SECOND FROM TIME '17:12:28.5');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">28.5</code>
</pre></dd><dt><span class="term"><code class="literal">timezone</code></span></dt><dd><p>
The time zone offset from UTC, measured in seconds. Positive values
correspond to time zones east of UTC, negative values to
zones west of UTC. (Technically,
<span class="productname">PostgreSQL</span> does not use UTC because
leap seconds are not handled.)
</p></dd><dt><span class="term"><code class="literal">timezone_hour</code></span></dt><dd><p>
The hour component of the time zone offset
</p></dd><dt><span class="term"><code class="literal">timezone_minute</code></span></dt><dd><p>
The minute component of the time zone offset
</p></dd><dt><span class="term"><code class="literal">week</code></span></dt><dd><p>
The number of the <acronym class="acronym">ISO</acronym> 8601 week-numbering week of
the year. By definition, ISO weeks start on Mondays and the first
week of a year contains January 4 of that year. In other words, the
first Thursday of a year is in week 1 of that year.
</p><p>
In the ISO week-numbering system, it is possible for early-January
dates to be part of the 52nd or 53rd week of the previous year, and for
late-December dates to be part of the first week of the next year.
For example, <code class="literal">2005-01-01</code> is part of the 53rd week of year
2004, and <code class="literal">2006-01-01</code> is part of the 52nd week of year
2005, while <code class="literal">2012-12-31</code> is part of the first week of 2013.
It's recommended to use the <code class="literal">isoyear</code> field together with
<code class="literal">week</code> to get consistent results.
</p><pre class="screen">
SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">7</code>
</pre></dd><dt><span class="term"><code class="literal">year</code></span></dt><dd><p>
The year field. Keep in mind there is no <code class="literal">0 AD</code>, so subtracting
<code class="literal">BC</code> years from <code class="literal">AD</code> years should be done with care.
</p><pre class="screen">
SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001</code>
</pre></dd></dl></div><p>
</p><div class="note"><h3 class="title">Note</h3><p>
When the input value is +/-Infinity, <code class="function">extract</code> returns
+/-Infinity for monotonically-increasing fields (<code class="literal">epoch</code>,
<code class="literal">julian</code>, <code class="literal">year</code>, <code class="literal">isoyear</code>,
<code class="literal">decade</code>, <code class="literal">century</code>, and <code class="literal">millennium</code>).
For other fields, NULL is returned. <span class="productname">PostgreSQL</span>
versions before 9.6 returned zero for all cases of infinite input.
</p></div><p>
The <code class="function">extract</code> function is primarily intended
for computational processing. For formatting date/time values for
display, see <a class="xref" href="functions-formatting.html" title="9.8. Data Type Formatting Functions">Section 9.8</a>.
</p><p>
The <code class="function">date_part</code> function is modeled on the traditional
<span class="productname">Ingres</span> equivalent to the
<acronym class="acronym">SQL</acronym>-standard function <code class="function">extract</code>:
</p><pre class="synopsis">
date_part('<em class="replaceable"><code>field</code></em>', <em class="replaceable"><code>source</code></em>)
</pre><p>
Note that here the <em class="replaceable"><code>field</code></em> parameter needs to
be a string value, not a name. The valid field names for
<code class="function">date_part</code> are the same as for
<code class="function">extract</code>.
</p><pre class="screen">
SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">16</code>
SELECT date_part('hour', INTERVAL '4 hours 3 minutes');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">4</code>
</pre></div><div class="sect2" id="FUNCTIONS-DATETIME-TRUNC"><div class="titlepage"><div><div><h3 class="title">9.9.2. <code class="function">date_trunc</code></h3></div></div></div><a id="id-1.5.8.14.13.2" class="indexterm"></a><p>
The function <code class="function">date_trunc</code> is conceptually
similar to the <code class="function">trunc</code> function for numbers.
</p><p>
</p><pre class="synopsis">
date_trunc('<em class="replaceable"><code>field</code></em>', <em class="replaceable"><code>source</code></em>)
</pre><p>
<em class="replaceable"><code>source</code></em> is a value expression of type
<code class="type">timestamp</code> or <code class="type">interval</code>.
(Values of type <code class="type">date</code> and
<code class="type">time</code> are cast automatically to <code class="type">timestamp</code> or
<code class="type">interval</code>, respectively.)
<em class="replaceable"><code>field</code></em> selects to which precision to
truncate the input value. The return value is of type
<code class="type">timestamp</code> or <code class="type">interval</code>
with all fields that are less significant than the
selected one set to zero (or one, for day and month).
</p><p>
Valid values for <em class="replaceable"><code>field</code></em> are:
</p><table border="0" summary="Simple list" class="simplelist"><tr><td><code class="literal">microseconds</code></td></tr><tr><td><code class="literal">milliseconds</code></td></tr><tr><td><code class="literal">second</code></td></tr><tr><td><code class="literal">minute</code></td></tr><tr><td><code class="literal">hour</code></td></tr><tr><td><code class="literal">day</code></td></tr><tr><td><code class="literal">week</code></td></tr><tr><td><code class="literal">month</code></td></tr><tr><td><code class="literal">quarter</code></td></tr><tr><td><code class="literal">year</code></td></tr><tr><td><code class="literal">decade</code></td></tr><tr><td><code class="literal">century</code></td></tr><tr><td><code class="literal">millennium</code></td></tr></table><p>
</p><p>
Examples:
</p><pre class="screen">
SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001-02-16 20:00:00</code>
SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001-01-01 00:00:00</code>
</pre><p>
</p></div><div class="sect2" id="FUNCTIONS-DATETIME-ZONECONVERT"><div class="titlepage"><div><div><h3 class="title">9.9.3. <code class="literal">AT TIME ZONE</code></h3></div></div></div><a id="id-1.5.8.14.14.2" class="indexterm"></a><a id="id-1.5.8.14.14.3" class="indexterm"></a><p>
The <code class="literal">AT TIME ZONE</code> converts time
stamp <span class="emphasis"><em>without time zone</em></span> to/from
time stamp <span class="emphasis"><em>with time zone</em></span>, and
<span class="emphasis"><em>time</em></span> values to different time zones. <a class="xref" href="functions-datetime.html#FUNCTIONS-DATETIME-ZONECONVERT-TABLE" title="Table 9.31. AT TIME ZONE Variants">Table 9.31</a> shows its variants.
</p><div class="table" id="FUNCTIONS-DATETIME-ZONECONVERT-TABLE"><p class="title"><strong>Table 9.31. <code class="literal">AT TIME ZONE</code> Variants</strong></p><div class="table-contents"><table class="table" summary="AT TIME ZONE Variants" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Expression</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>
<code class="literal"><code class="type">timestamp without time zone</code> AT TIME ZONE <em class="replaceable"><code>zone</code></em></code>
</td><td><code class="type">timestamp with time zone</code></td><td>Treat given time stamp <span class="emphasis"><em>without time zone</em></span> as located in the specified time zone</td></tr><tr><td>
<code class="literal"><code class="type">timestamp with time zone</code> AT TIME ZONE <em class="replaceable"><code>zone</code></em></code>
</td><td><code class="type">timestamp without time zone</code></td><td>Convert given time stamp <span class="emphasis"><em>with time zone</em></span> to the new time
zone, with no time zone designation</td></tr><tr><td>
<code class="literal"><code class="type">time with time zone</code> AT TIME ZONE <em class="replaceable"><code>zone</code></em></code>
</td><td><code class="type">time with time zone</code></td><td>Convert given time <span class="emphasis"><em>with time zone</em></span> to the new time zone</td></tr></tbody></table></div></div><br class="table-break" /><p>
In these expressions, the desired time zone <em class="replaceable"><code>zone</code></em> can be
specified either as a text string (e.g., <code class="literal">'America/Los_Angeles'</code>)
or as an interval (e.g., <code class="literal">INTERVAL '-08:00'</code>).
In the text case, a time zone name can be specified in any of the ways
described in <a class="xref" href="datatype-datetime.html#DATATYPE-TIMEZONES" title="8.5.3. Time Zones">Section 8.5.3</a>.
</p><p>
Examples (assuming the local time zone is <code class="literal">America/Los_Angeles</code>):
</p><pre class="screen">
SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'America/Denver';
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001-02-16 19:38:40-08</code>
SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'America/Denver';
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001-02-16 18:38:40</code>
SELECT TIMESTAMP '2001-02-16 20:38:40-05' AT TIME ZONE 'Asia/Tokyo' AT TIME ZONE 'America/Chicago';
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001-02-16 05:38:40</code>
</pre><p>
The first example adds a time zone to a value that lacks it, and
displays the value using the current <code class="varname">TimeZone</code>
setting. The second example shifts the time stamp with time zone value
to the specified time zone, and returns the value without a time zone.
This allows storage and display of values different from the current
<code class="varname">TimeZone</code> setting. The third example converts
Tokyo time to Chicago time. Converting <span class="emphasis"><em>time</em></span>
values to other time zones uses the currently active time zone rules
since no date is supplied.
</p><p>
The function <code class="literal"><code class="function">timezone</code>(<em class="replaceable"><code>zone</code></em>,
<em class="replaceable"><code>timestamp</code></em>)</code> is equivalent to the SQL-conforming construct
<code class="literal"><em class="replaceable"><code>timestamp</code></em> AT TIME ZONE
<em class="replaceable"><code>zone</code></em></code>.
</p></div><div class="sect2" id="FUNCTIONS-DATETIME-CURRENT"><div class="titlepage"><div><div><h3 class="title">9.9.4. Current Date/Time</h3></div></div></div><a id="id-1.5.8.14.15.2" class="indexterm"></a><a id="id-1.5.8.14.15.3" class="indexterm"></a><p>
<span class="productname">PostgreSQL</span> provides a number of functions
that return values related to the current date and time. These
SQL-standard functions all return values based on the start time of
the current transaction:
</p><pre class="synopsis">
CURRENT_DATE
CURRENT_TIME
CURRENT_TIMESTAMP
CURRENT_TIME(<em class="replaceable"><code>precision</code></em>)
CURRENT_TIMESTAMP(<em class="replaceable"><code>precision</code></em>)
LOCALTIME
LOCALTIMESTAMP
LOCALTIME(<em class="replaceable"><code>precision</code></em>)
LOCALTIMESTAMP(<em class="replaceable"><code>precision</code></em>)
</pre><p>
</p><p>
<code class="function">CURRENT_TIME</code> and
<code class="function">CURRENT_TIMESTAMP</code> deliver values with time zone;
<code class="function">LOCALTIME</code> and
<code class="function">LOCALTIMESTAMP</code> deliver values without time zone.
</p><p>
<code class="function">CURRENT_TIME</code>,
<code class="function">CURRENT_TIMESTAMP</code>,
<code class="function">LOCALTIME</code>, and
<code class="function">LOCALTIMESTAMP</code>
can optionally take
a precision parameter, which causes the result to be rounded
to that many fractional digits in the seconds field. Without a precision parameter,
the result is given to the full available precision.
</p><p>
Some examples:
</p><pre class="screen">
SELECT CURRENT_TIME;
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">14:39:53.662522-05</code>
SELECT CURRENT_DATE;
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001-12-23</code>
SELECT CURRENT_TIMESTAMP;
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001-12-23 14:39:53.662522-05</code>
SELECT CURRENT_TIMESTAMP(2);
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001-12-23 14:39:53.66-05</code>
SELECT LOCALTIMESTAMP;
<em class="lineannotation"><span class="lineannotation">Result: </span></em><code class="computeroutput">2001-12-23 14:39:53.662522</code>
</pre><p>
</p><p>
Since these functions return
the start time of the current transaction, their values do not
change during the transaction. This is considered a feature:
the intent is to allow a single transaction to have a consistent
notion of the <span class="quote">“<span class="quote">current</span>”</span> time, so that multiple
modifications within the same transaction bear the same
time stamp.
</p><div class="note"><h3 class="title">Note</h3><p>
Other database systems might advance these values more
frequently.
</p></div><p>
<span class="productname">PostgreSQL</span> also provides functions that
return the start time of the current statement, as well as the actual
current time at the instant the function is called. The complete list
of non-SQL-standard time functions is:
</p><pre class="synopsis">
transaction_timestamp()
statement_timestamp()
clock_timestamp()
timeofday()
now()
</pre><p>
</p><p>
<code class="function">transaction_timestamp()</code> is equivalent to
<code class="function">CURRENT_TIMESTAMP</code>, but is named to clearly reflect
what it returns.
<code class="function">statement_timestamp()</code> returns the start time of the current
statement (more specifically, the time of receipt of the latest command
message from the client).
<code class="function">statement_timestamp()</code> and <code class="function">transaction_timestamp()</code>
return the same value during the first command of a transaction, but might
differ during subsequent commands.
<code class="function">clock_timestamp()</code> returns the actual current time, and
therefore its value changes even within a single SQL command.
<code class="function">timeofday()</code> is a historical
<span class="productname">PostgreSQL</span> function. Like
<code class="function">clock_timestamp()</code>, it returns the actual current time,
but as a formatted <code class="type">text</code> string rather than a <code class="type">timestamp
with time zone</code> value.
<code class="function">now()</code> is a traditional <span class="productname">PostgreSQL</span>
equivalent to <code class="function">transaction_timestamp()</code>.
</p><p>
All the date/time data types also accept the special literal value
<code class="literal">now</code> to specify the current date and time (again,
interpreted as the transaction start time). Thus,
the following three all return the same result:
</p><pre class="programlisting">
SELECT CURRENT_TIMESTAMP;
SELECT now();
SELECT TIMESTAMP 'now'; -- incorrect for use with DEFAULT
</pre><p>
</p><div class="tip"><h3 class="title">Tip</h3><p>
You do not want to use the third form when specifying a <code class="literal">DEFAULT</code>
clause while creating a table. The system will convert <code class="literal">now</code>
to a <code class="type">timestamp</code> as soon as the constant is parsed, so that when
the default value is needed,
the time of the table creation would be used! The first two
forms will not be evaluated until the default value is used,
because they are function calls. Thus they will give the desired
behavior of defaulting to the time of row insertion.
</p></div></div><div class="sect2" id="FUNCTIONS-DATETIME-DELAY"><div class="titlepage"><div><div><h3 class="title">9.9.5. Delaying Execution</h3></div></div></div><a id="id-1.5.8.14.16.2" class="indexterm"></a><a id="id-1.5.8.14.16.3" class="indexterm"></a><a id="id-1.5.8.14.16.4" class="indexterm"></a><a id="id-1.5.8.14.16.5" class="indexterm"></a><a id="id-1.5.8.14.16.6" class="indexterm"></a><p>
The following functions are available to delay execution of the server
process:
</p><pre class="synopsis">
pg_sleep(<em class="replaceable"><code>seconds</code></em>)
pg_sleep_for(<code class="type">interval</code>)
pg_sleep_until(<code class="type">timestamp with time zone</code>)
</pre><p>
<code class="function">pg_sleep</code> makes the current session's process
sleep until <em class="replaceable"><code>seconds</code></em> seconds have
elapsed. <em class="replaceable"><code>seconds</code></em> is a value of type
<code class="type">double precision</code>, so fractional-second delays can be specified.
<code class="function">pg_sleep_for</code> is a convenience function for larger
sleep times specified as an <code class="type">interval</code>.
<code class="function">pg_sleep_until</code> is a convenience function for when
a specific wake-up time is desired.
For example:
</p><pre class="programlisting">
SELECT pg_sleep(1.5);
SELECT pg_sleep_for('5 minutes');
SELECT pg_sleep_until('tomorrow 03:00');
</pre><p>
</p><div class="note"><h3 class="title">Note</h3><p>
The effective resolution of the sleep interval is platform-specific;
0.01 seconds is a common value. The sleep delay will be at least as long
as specified. It might be longer depending on factors such as server load.
In particular, <code class="function">pg_sleep_until</code> is not guaranteed to
wake up exactly at the specified time, but it will not wake up any earlier.
</p></div><div class="warning"><h3 class="title">Warning</h3><p>
Make sure that your session does not hold more locks than necessary
when calling <code class="function">pg_sleep</code> or its variants. Otherwise
other sessions might have to wait for your sleeping process, slowing down
the entire system.
</p></div></div><div class="footnotes"><br /><hr style="width:100; text-align:left;margin-left: 0" /><div id="ftn.id-1.5.8.14.12.5.11.16.2.1.1" class="footnote"><p><a href="#id-1.5.8.14.12.5.11.16.2.1.1" class="simpara"><sup class="simpara">[7] </sup></a>60 if leap seconds are
implemented by the operating system</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="functions-formatting.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="functions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="functions-enum.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">9.8. Data Type Formatting Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 9.10. Enum Support Functions</td></tr></table></div></body></html>
