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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="FUNCTIONS-DATETIME"
>9.9. Date/Time Functions and Operators</A
></H1
><P
> <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-TABLE"
>Table 9-26</A
> shows the available
functions for date/time value processing, with details appearing in
the following subsections. <A
HREF="functions-datetime.html#OPERATORS-DATETIME-TABLE"
>Table 9-25</A
> illustrates the behaviors of
the basic arithmetic operators (<TT
CLASS="LITERAL"
>+</TT
>,
<TT
CLASS="LITERAL"
>*</TT
>, etc.). For formatting functions, refer to
<A
HREF="functions-formatting.html"
>Section 9.8</A
>. You should be familiar with
the background information on date/time data types from <A
HREF="datatype-datetime.html"
>Section 8.5</A
>.
</P
><P
> All the functions and operators described below that take <TT
CLASS="TYPE"
>time</TT
> or <TT
CLASS="TYPE"
>timestamp</TT
>
inputs actually come in two variants: one that takes <TT
CLASS="TYPE"
>time with time zone</TT
> or <TT
CLASS="TYPE"
>timestamp
with time zone</TT
>, and one that takes <TT
CLASS="TYPE"
>time without time zone</TT
> or <TT
CLASS="TYPE"
>timestamp without time zone</TT
>.
For brevity, these variants are not shown separately. Also, the
<TT
CLASS="LITERAL"
>+</TT
> and <TT
CLASS="LITERAL"
>*</TT
> 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"
><A
NAME="OPERATORS-DATETIME-TABLE"
></A
><P
><B
>Table 9-25. Date/Time Operators</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><THEAD
><TR
><TH
>Operator</TH
><TH
>Example</TH
><TH
>Result</TH
></TR
></THEAD
><TBODY
><TR
><TD
> <TT
CLASS="LITERAL"
>+</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>date '2001-09-28' + integer '7'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>date '2001-10-05'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>+</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>date '2001-09-28' + interval '1 hour'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>timestamp '2001-09-28 01:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>+</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>date '2001-09-28' + time '03:00'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>timestamp '2001-09-28 03:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>+</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>interval '1 day' + interval '1 hour'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>interval '1 day 01:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>+</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>timestamp '2001-09-28 01:00' + interval '23 hours'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>timestamp '2001-09-29 00:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>+</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>time '01:00' + interval '3 hours'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>time '04:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>-</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>- interval '23 hours'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>interval '-23:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>-</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>date '2001-10-01' - date '2001-09-28'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>integer '3'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>-</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>date '2001-10-01' - integer '7'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>date '2001-09-24'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>-</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>date '2001-09-28' - interval '1 hour'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>timestamp '2001-09-27 23:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>-</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>time '05:00' - time '03:00'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>interval '02:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>-</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>time '05:00' - interval '2 hours'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>time '03:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>-</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>timestamp '2001-09-28 23:00' - interval '23 hours'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>timestamp '2001-09-28 00:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>-</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>interval '1 day' - interval '1 hour'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>interval '23:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>-</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>timestamp '2001-09-29 03:00' - timestamp '2001-09-27 12:00'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>interval '1 day 15:00'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>*</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>interval '1 hour' * double precision '3.5'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>interval '03:30'</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>/</TT
> </TD
><TD
><TT
CLASS="LITERAL"
>interval '1 hour' / double precision '1.5'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>interval '00:40'</TT
></TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="FUNCTIONS-DATETIME-TABLE"
></A
><P
><B
>Table 9-26. Date/Time Functions</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><COL><THEAD
><TR
><TH
>Function</TH
><TH
>Return Type</TH
><TH
>Description</TH
><TH
>Example</TH
><TH
>Result</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>age</CODE
>(<TT
CLASS="TYPE"
>timestamp</TT
>, <TT
CLASS="TYPE"
>timestamp</TT
>)</TT
></TD
><TD
><TT
CLASS="TYPE"
>interval</TT
></TD
><TD
>Subtract arguments, producing a <SPAN
CLASS="QUOTE"
>"symbolic"</SPAN
> result that
uses years and months</TD
><TD
><TT
CLASS="LITERAL"
>age(timestamp '2001-04-10', timestamp '1957-06-13')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>43 years 9 mons 27 days</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>age</CODE
>(<TT
CLASS="TYPE"
>timestamp</TT
>)</TT
></TD
><TD
><TT
CLASS="TYPE"
>interval</TT
></TD
><TD
>Subtract from <CODE
CLASS="FUNCTION"
>current_date</CODE
></TD
><TD
><TT
CLASS="LITERAL"
>age(timestamp '1957-06-13')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>43 years 8 mons 3 days</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>current_date</CODE
></TT
></TD
><TD
><TT
CLASS="TYPE"
>date</TT
></TD
><TD
>Today's date; see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT"
>Section 9.9.4</A
>
</TD
><TD
> </TD
><TD
> </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>current_time</CODE
></TT
></TD
><TD
><TT
CLASS="TYPE"
>time with time zone</TT
></TD
><TD
>Time of day; see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT"
>Section 9.9.4</A
>
</TD
><TD
> </TD
><TD
> </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>current_timestamp</CODE
></TT
></TD
><TD
><TT
CLASS="TYPE"
>timestamp with time zone</TT
></TD
><TD
>Date and time; see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT"
>Section 9.9.4</A
>
</TD
><TD
> </TD
><TD
> </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>date_part</CODE
>(<TT
CLASS="TYPE"
>text</TT
>, <TT
CLASS="TYPE"
>timestamp</TT
>)</TT
></TD
><TD
><TT
CLASS="TYPE"
>double precision</TT
></TD
><TD
>Get subfield (equivalent to
<CODE
CLASS="FUNCTION"
>extract</CODE
>); see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT"
>Section 9.9.1</A
>
</TD
><TD
><TT
CLASS="LITERAL"
>date_part('hour', timestamp '2001-02-16 20:38:40')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>20</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>date_part</CODE
>(<TT
CLASS="TYPE"
>text</TT
>, <TT
CLASS="TYPE"
>interval</TT
>)</TT
></TD
><TD
><TT
CLASS="TYPE"
>double precision</TT
></TD
><TD
>Get subfield (equivalent to
<CODE
CLASS="FUNCTION"
>extract</CODE
>); see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT"
>Section 9.9.1</A
>
</TD
><TD
><TT
CLASS="LITERAL"
>date_part('month', interval '2 years 3 months')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>3</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>date_trunc</CODE
>(<TT
CLASS="TYPE"
>text</TT
>, <TT
CLASS="TYPE"
>timestamp</TT
>)</TT
></TD
><TD
><TT
CLASS="TYPE"
>timestamp</TT
></TD
><TD
>Truncate to specified precision; see also <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-TRUNC"
>Section 9.9.2</A
>
</TD
><TD
><TT
CLASS="LITERAL"
>date_trunc('hour', timestamp '2001-02-16 20:38:40')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>2001-02-16 20:00:00</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>extract</CODE
>(<TT
CLASS="PARAMETER"
>field</TT
> from
<TT
CLASS="TYPE"
>timestamp</TT
>)</TT
></TD
><TD
><TT
CLASS="TYPE"
>double precision</TT
></TD
><TD
>Get subfield; see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT"
>Section 9.9.1</A
>
</TD
><TD
><TT
CLASS="LITERAL"
>extract(hour from timestamp '2001-02-16 20:38:40')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>20</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>extract</CODE
>(<TT
CLASS="PARAMETER"
>field</TT
> from
<TT
CLASS="TYPE"
>interval</TT
>)</TT
></TD
><TD
><TT
CLASS="TYPE"
>double precision</TT
></TD
><TD
>Get subfield; see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT"
>Section 9.9.1</A
>
</TD
><TD
><TT
CLASS="LITERAL"
>extract(month from interval '2 years 3 months')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>3</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>isfinite</CODE
>(<TT
CLASS="TYPE"
>timestamp</TT
>)</TT
></TD
><TD
><TT
CLASS="TYPE"
>boolean</TT
></TD
><TD
>Test for finite time stamp (not equal to infinity)</TD
><TD
><TT
CLASS="LITERAL"
>isfinite(timestamp '2001-02-16 21:28:30')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>true</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>isfinite</CODE
>(<TT
CLASS="TYPE"
>interval</TT
>)</TT
></TD
><TD
><TT
CLASS="TYPE"
>boolean</TT
></TD
><TD
>Test for finite interval</TD
><TD
><TT
CLASS="LITERAL"
>isfinite(interval '4 hours')</TT
></TD
><TD
><TT
CLASS="LITERAL"
>true</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>localtime</CODE
></TT
></TD
><TD
><TT
CLASS="TYPE"
>time</TT
></TD
><TD
>Time of day; see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT"
>Section 9.9.4</A
>
</TD
><TD
> </TD
><TD
> </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>localtimestamp</CODE
></TT
></TD
><TD
><TT
CLASS="TYPE"
>timestamp</TT
></TD
><TD
>Date and time; see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT"
>Section 9.9.4</A
>
</TD
><TD
> </TD
><TD
> </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>now</CODE
>()</TT
></TD
><TD
><TT
CLASS="TYPE"
>timestamp with time zone</TT
></TD
><TD
>Current date and time (equivalent to
<CODE
CLASS="FUNCTION"
>current_timestamp</CODE
>); see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT"
>Section 9.9.4</A
>
</TD
><TD
> </TD
><TD
> </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>timeofday()</CODE
></TT
></TD
><TD
><TT
CLASS="TYPE"
>text</TT
></TD
><TD
>Current date and time; see <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-CURRENT"
>Section 9.9.4</A
>
</TD
><TD
> </TD
><TD
> </TD
></TR
></TBODY
></TABLE
></DIV
><P
> In addition to these functions, the SQL <TT
CLASS="LITERAL"
>OVERLAPS</TT
> operator is
supported:
</P><PRE
CLASS="SYNOPSIS"
>( <TT
CLASS="REPLACEABLE"
><I
>start1</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>end1</I
></TT
> ) OVERLAPS ( <TT
CLASS="REPLACEABLE"
><I
>start2</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>end2</I
></TT
> )
( <TT
CLASS="REPLACEABLE"
><I
>start1</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>length1</I
></TT
> ) OVERLAPS ( <TT
CLASS="REPLACEABLE"
><I
>start2</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>length2</I
></TT
> )</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.
</P
><PRE
CLASS="SCREEN"
>SELECT (DATE '2001-02-16', DATE '2001-12-21') OVERLAPS
(DATE '2001-10-30', DATE '2002-10-30');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>true</SAMP
>
SELECT (DATE '2001-02-16', INTERVAL '100 days') OVERLAPS
(DATE '2001-10-30', DATE '2002-10-30');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>false</SAMP
></PRE
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="FUNCTIONS-DATETIME-EXTRACT"
>9.9.1. <CODE
CLASS="FUNCTION"
>EXTRACT</CODE
>, <CODE
CLASS="FUNCTION"
>date_part</CODE
></A
></H2
><PRE
CLASS="SYNOPSIS"
>EXTRACT (<TT
CLASS="REPLACEABLE"
><I
>field</I
></TT
> FROM <TT
CLASS="REPLACEABLE"
><I
>source</I
></TT
>)</PRE
><P
> The <CODE
CLASS="FUNCTION"
>extract</CODE
> function retrieves subfields
such as year or hour from date/time values.
<TT
CLASS="REPLACEABLE"
><I
>source</I
></TT
> must be a value expression of
type <TT
CLASS="TYPE"
>timestamp</TT
>, <TT
CLASS="TYPE"
>time</TT
>, or <TT
CLASS="TYPE"
>interval</TT
>.
(Expressions of type <TT
CLASS="TYPE"
>date</TT
> will
be cast to <TT
CLASS="TYPE"
>timestamp</TT
> and can therefore be used as
well.) <TT
CLASS="REPLACEABLE"
><I
>field</I
></TT
> 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
<TT
CLASS="TYPE"
>double precision</TT
>.
The following are valid field names:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>century</TT
></DT
><DD
><P
> The century
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(CENTURY FROM TIMESTAMP '2000-12-16 12:21:13');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>20</SAMP
>
SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>21</SAMP
></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 to 1.
If you disagree with this, please write your complaint to:
Pope, Cathedral Saint-Peter of Roma, Vatican.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> releases before 8.0 did not
follow the conventional numbering of centuries, but just returned
the year field divided by 100.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>day</TT
></DT
><DD
><P
> The day (of the month) field (1 - 31)
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>16</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>decade</TT
></DT
><DD
><P
> The year field divided by 10
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(DECADE FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>200</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>dow</TT
></DT
><DD
><P
> The day of the week (0 - 6; Sunday is 0) (for
<TT
CLASS="TYPE"
>timestamp</TT
> values only)
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>5</SAMP
></PRE
><P
> Note that <CODE
CLASS="FUNCTION"
>extract</CODE
>'s day of the week numbering is
different from that of the <CODE
CLASS="FUNCTION"
>to_char</CODE
> function.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>doy</TT
></DT
><DD
><P
> The day of the year (1 - 365/366) (for <TT
CLASS="TYPE"
>timestamp</TT
> values only)
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>47</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>epoch</TT
></DT
><DD
><P
> For <TT
CLASS="TYPE"
>date</TT
> and <TT
CLASS="TYPE"
>timestamp</TT
> values, the
number of seconds since 1970-01-01 00:00:00-00 (can be negative);
for <TT
CLASS="TYPE"
>interval</TT
> values, the total number
of seconds in the interval
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(EPOCH FROM TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-08');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>982384720</SAMP
>
SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>442800</SAMP
></PRE
><P
> Here is how you can convert an epoch value back to a time
stamp:
</P
><PRE
CLASS="SCREEN"
>SELECT TIMESTAMP WITH TIME ZONE 'epoch' + 982384720 * INTERVAL '1 second';</PRE
></DD
><DT
><TT
CLASS="LITERAL"
>hour</TT
></DT
><DD
><P
> The hour field (0 - 23)
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>20</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>microseconds</TT
></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');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>28500000</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>millennium</TT
></DT
><DD
><P
> The millennium
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>3</SAMP
></PRE
><P
> Years in the 1900s are in the second millennium.
The third millennium starts January 1, 2001.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> releases before 8.0 did not
follow the conventional numbering of millennia, but just returned
the year field divided by 1000.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>milliseconds</TT
></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');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>28500</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>minute</TT
></DT
><DD
><P
> The minutes field (0 - 59)
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>38</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>month</TT
></DT
><DD
><P
> For <TT
CLASS="TYPE"
>timestamp</TT
> values, the number of the month
within the year (1 - 12) ; for <TT
CLASS="TYPE"
>interval</TT
> values
the number of months, modulo 12 (0 - 11)
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(MONTH FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>2</SAMP
>
SELECT EXTRACT(MONTH FROM INTERVAL '2 years 3 months');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>3</SAMP
>
SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>1</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>quarter</TT
></DT
><DD
><P
> The quarter of the year (1 - 4) that the day is in (for
<TT
CLASS="TYPE"
>timestamp</TT
> values only)
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>1</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>second</TT
></DT
><DD
><P
> The seconds field, including fractional parts (0 -
59<A
NAME="AEN10805"
HREF="#FTN.AEN10805"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
>)
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(SECOND FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>40</SAMP
>
SELECT EXTRACT(SECOND FROM TIME '17:12:28.5');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>28.5</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>timezone</TT
></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.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>timezone_hour</TT
></DT
><DD
><P
> The hour component of the time zone offset
</P
></DD
><DT
><TT
CLASS="LITERAL"
>timezone_minute</TT
></DT
><DD
><P
> The minute component of the time zone offset
</P
></DD
><DT
><TT
CLASS="LITERAL"
>week</TT
></DT
><DD
><P
> The number of the week of the year that the day is in. By definition
(<ACRONYM
CLASS="ACRONYM"
>ISO</ACRONYM
> 8601), the first week of a year
contains January 4 of that year. (The <ACRONYM
CLASS="ACRONYM"
>ISO</ACRONYM
>-8601
week starts on Monday.) In other words, the first Thursday of
a year is in week 1 of that year. (for <TT
CLASS="TYPE"
>timestamp</TT
> values only)
</P
><P
> Because of this, it is possible for early January dates to be part of the
52nd or 53rd week of the previous year. For example, <TT
CLASS="LITERAL"
>2005-01-01</TT
>
is part of the 53rd week of year 2004, and <TT
CLASS="LITERAL"
>2006-01-01</TT
> is part of
the 52nd week of year 2005.
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>7</SAMP
></PRE
></DD
><DT
><TT
CLASS="LITERAL"
>year</TT
></DT
><DD
><P
> The year field. Keep in mind there is no <TT
CLASS="LITERAL"
>0 AD</TT
>, so subtracting
<TT
CLASS="LITERAL"
>BC</TT
> years from <TT
CLASS="LITERAL"
>AD</TT
> years should be done with care.
</P
><PRE
CLASS="SCREEN"
>SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>2001</SAMP
></PRE
></DD
></DL
></DIV
><P>
</P
><P
> The <CODE
CLASS="FUNCTION"
>extract</CODE
> function is primarily intended
for computational processing. For formatting date/time values for
display, see <A
HREF="functions-formatting.html"
>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('<TT
CLASS="REPLACEABLE"
><I
>field</I
></TT
>', <TT
CLASS="REPLACEABLE"
><I
>source</I
></TT
>)</PRE
><P>
Note that here the <TT
CLASS="REPLACEABLE"
><I
>field</I
></TT
> 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');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>16</SAMP
>
SELECT date_part('hour', INTERVAL '4 hours 3 minutes');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>4</SAMP
></PRE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="FUNCTIONS-DATETIME-TRUNC"
>9.9.2. <CODE
CLASS="FUNCTION"
>date_trunc</CODE
></A
></H2
><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('<TT
CLASS="REPLACEABLE"
><I
>field</I
></TT
>', <TT
CLASS="REPLACEABLE"
><I
>source</I
></TT
>)</PRE
><P>
<TT
CLASS="REPLACEABLE"
><I
>source</I
></TT
> is a value expression of type
<TT
CLASS="TYPE"
>timestamp</TT
> or <TT
CLASS="TYPE"
>interval</TT
>.
(Values of type <TT
CLASS="TYPE"
>date</TT
> and
<TT
CLASS="TYPE"
>time</TT
> are cast automatically, to <TT
CLASS="TYPE"
>timestamp</TT
> or
<TT
CLASS="TYPE"
>interval</TT
> respectively.)
<TT
CLASS="REPLACEABLE"
><I
>field</I
></TT
> selects to which precision to
truncate the input value. The return value is of type
<TT
CLASS="TYPE"
>timestamp</TT
> or <TT
CLASS="TYPE"
>interval</TT
>
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 <TT
CLASS="REPLACEABLE"
><I
>field</I
></TT
> are:
<P
></P
><TABLE
BORDER="0"
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
>microseconds</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>milliseconds</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>second</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>minute</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>hour</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>day</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>week</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>month</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>quarter</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>year</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>decade</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>century</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>millennium</TT
></TD
></TR
></TBODY
></TABLE
><P
></P
>
</P
><P
> Examples:
</P><PRE
CLASS="SCREEN"
>SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>2001-02-16 20:00:00</SAMP
>
SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>2001-01-01 00:00:00</SAMP
></PRE
><P>
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="FUNCTIONS-DATETIME-ZONECONVERT"
>9.9.3. <TT
CLASS="LITERAL"
>AT TIME ZONE</TT
></A
></H2
><A
NAME="AEN10929"
></A
><P
> The <TT
CLASS="LITERAL"
>AT TIME ZONE</TT
> construct allows conversions
of time stamps to different time zones. <A
HREF="functions-datetime.html#FUNCTIONS-DATETIME-ZONECONVERT-TABLE"
>Table 9-27</A
> shows its
variants.
</P
><DIV
CLASS="TABLE"
><A
NAME="FUNCTIONS-DATETIME-ZONECONVERT-TABLE"
></A
><P
><B
>Table 9-27. <TT
CLASS="LITERAL"
>AT TIME ZONE</TT
> Variants</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><THEAD
><TR
><TH
>Expression</TH
><TH
>Return Type</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
> <TT
CLASS="LITERAL"
><TT
CLASS="TYPE"
>timestamp without time zone</TT
> AT TIME ZONE <TT
CLASS="REPLACEABLE"
><I
>zone</I
></TT
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>timestamp with time zone</TT
></TD
><TD
>Convert local time in given time zone to UTC</TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
><TT
CLASS="TYPE"
>timestamp with time zone</TT
> AT TIME ZONE <TT
CLASS="REPLACEABLE"
><I
>zone</I
></TT
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>timestamp without time zone</TT
></TD
><TD
>Convert UTC to local time in given time zone</TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
><TT
CLASS="TYPE"
>time with time zone</TT
> AT TIME ZONE <TT
CLASS="REPLACEABLE"
><I
>zone</I
></TT
></TT
>
</TD
><TD
><TT
CLASS="TYPE"
>time with time zone</TT
></TD
><TD
>Convert local time across time zones</TD
></TR
></TBODY
></TABLE
></DIV
><P
> In these expressions, the desired time zone <TT
CLASS="REPLACEABLE"
><I
>zone</I
></TT
> can be
specified either as a text string (e.g., <TT
CLASS="LITERAL"
>'PST'</TT
>)
or as an interval (e.g., <TT
CLASS="LITERAL"
>INTERVAL '-08:00'</TT
>).
In the text case, the available zone names are those shown in
<A
HREF="datetime-keywords.html#DATETIME-TIMEZONE-INPUT-TABLE"
>Table B-4</A
>. (It would be useful
to support the more general names shown in
<A
HREF="datetime-keywords.html#DATETIME-TIMEZONE-SET-TABLE"
>Table B-6</A
>, but this is not yet
implemented.)
</P
><P
> Examples (supposing that the local time zone is <TT
CLASS="LITERAL"
>PST8PDT</TT
>):
</P><PRE
CLASS="SCREEN"
>SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'MST';
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>2001-02-16 19:38:40-08</SAMP
>
SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'MST';
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>2001-02-16 18:38:40</SAMP
></PRE
><P>
The first example takes a zone-less time stamp and interprets it as MST time
(UTC-7) to produce a UTC time stamp, which is then rotated to PST (UTC-8)
for display. The second example takes a time stamp specified in EST
(UTC-5) and converts it to local time in MST (UTC-7).
</P
><P
> The function <TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>timezone</CODE
>(<TT
CLASS="REPLACEABLE"
><I
>zone</I
></TT
>,
<TT
CLASS="REPLACEABLE"
><I
>timestamp</I
></TT
>)</TT
> is equivalent to the SQL-conforming construct
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>timestamp</I
></TT
> AT TIME ZONE
<TT
CLASS="REPLACEABLE"
><I
>zone</I
></TT
></TT
>.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="FUNCTIONS-DATETIME-CURRENT"
>9.9.4. Current Date/Time</A
></H2
><A
NAME="AEN10992"
></A
><A
NAME="AEN10995"
></A
><P
> The following functions are available to obtain the current date and/or
time:
</P><PRE
CLASS="SYNOPSIS"
>CURRENT_DATE
CURRENT_TIME
CURRENT_TIMESTAMP
CURRENT_TIME ( <TT
CLASS="REPLACEABLE"
><I
>precision</I
></TT
> )
CURRENT_TIMESTAMP ( <TT
CLASS="REPLACEABLE"
><I
>precision</I
></TT
> )
LOCALTIME
LOCALTIMESTAMP
LOCALTIME ( <TT
CLASS="REPLACEABLE"
><I
>precision</I
></TT
> )
LOCALTIMESTAMP ( <TT
CLASS="REPLACEABLE"
><I
>precision</I
></TT
> )</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 be given
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
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> Prior to <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 7.2, the precision
parameters were unimplemented, and the result was always given
in integer seconds.
</P
></BLOCKQUOTE
></DIV
><P
> Some examples:
</P><PRE
CLASS="SCREEN"
>SELECT CURRENT_TIME;
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>14:39:53.662522-05</SAMP
>
SELECT CURRENT_DATE;
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>2001-12-23</SAMP
>
SELECT CURRENT_TIMESTAMP;
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>2001-12-23 14:39:53.662522-05</SAMP
>
SELECT CURRENT_TIMESTAMP(2);
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>2001-12-23 14:39:53.66-05</SAMP
>
SELECT LOCALTIMESTAMP;
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>2001-12-23 14:39:53.662522</SAMP
></PRE
><P>
</P
><P
> The function <CODE
CLASS="FUNCTION"
>now()</CODE
> is the traditional
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> equivalent to
<CODE
CLASS="FUNCTION"
>CURRENT_TIMESTAMP</CODE
>.
</P
><P
> There is also the function <CODE
CLASS="FUNCTION"
>timeofday()</CODE
>, which for historical
reasons returns a <TT
CLASS="TYPE"
>text</TT
> string rather than a <TT
CLASS="TYPE"
>timestamp</TT
> value:
</P><PRE
CLASS="SCREEN"
>SELECT timeofday();
<I
CLASS="LINEANNOTATION"
>Result: </I
><SAMP
CLASS="COMPUTEROUTPUT"
>Sat Feb 17 19:07:32.000126 2001 EST</SAMP
></PRE
><P>
</P
><P
> It is important to know that
<CODE
CLASS="FUNCTION"
>CURRENT_TIMESTAMP</CODE
> and related 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"
>"current"</SPAN
> time, so that multiple
modifications within the same transaction bear the same
time stamp. <CODE
CLASS="FUNCTION"
>timeofday()</CODE
>
returns the wall-clock time and does advance during transactions.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> Other database systems may advance these values more
frequently.
</P
></BLOCKQUOTE
></DIV
><P
> All the date/time data types also accept the special literal value
<TT
CLASS="LITERAL"
>now</TT
> to specify the current date and time. Thus,
the following three all return the same result:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT CURRENT_TIMESTAMP;
SELECT now();
SELECT TIMESTAMP 'now';</PRE
><P>
</P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
> You do not want to use the third form when specifying a <TT
CLASS="LITERAL"
>DEFAULT</TT
>
clause while creating a table. The system will convert <TT
CLASS="LITERAL"
>now</TT
>
to a <TT
CLASS="TYPE"
>timestamp</TT
> 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
></BLOCKQUOTE
></DIV
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
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>60 if leap seconds are
implemented by the operating system</P
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