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Enhance documentation of date/time functions. Add extract, current_date, 

current_time, current_timestamp.  Add more examples.  Remove age(), because
it doesn't work like it is documented, and no one could explain it to me.
This commit is contained in:
Peter Eisentraut 2001-02-18 17:17:17 +00:00
parent b9c7d371ed
commit 48d03278a2
1 changed files with 611 additions and 88 deletions
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doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.51 2001/02/12 14:21:27 momjian Exp $ -->
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.52 2001/02/18 17:17:17 petere Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -17,8 +17,8 @@
If you are concerned about portability then take note that most of
the functions and operators described in this chapter, with the
exception of the most trivial arithmetic and comparison operators
and some explicitly marked functions, are not specified by the SQL
standard. However, many other RDBMS packages provide a lot of the
and some explicitly marked functions, are not specified by the <acronym>SQL</acronym>
standard. However, many other <acronym>RDBMS</acronym> packages provide a lot of the
same or similar functions, and some of the ones provided in
<productname>Postgres</productname> have in fact been inspired by
other implementations.
@ -37,7 +37,7 @@
<member>NOT</member>
</simplelist>
SQL uses a three-valued boolean logic where NULL represents
<acronym>SQL</acronym> uses a three-valued Boolean logic where NULL represents
<quote>unknown</quote>. Observe the following truth tables:
<informaltable>
@ -179,9 +179,9 @@
<para>
Comparison operators are available for all data types where this
makes sense. All comparison operators are binary operators that
return boolean values; expressions like <literal>1 &lt; 2 &lt;
3</literal> are not valid (because there is no
<literal>&lt;</literal> operator to compare a boolean with
return values of type <type>boolean</type>; expressions like
<literal>1 &lt; 2 &lt; 3</literal> are not valid (because there is
no <literal>&lt;</literal> operator to compare a Boolean value with
<literal>3</literal>).
</para>
@ -685,7 +685,7 @@
</para>
<para>
SQL defines some string functions with a special syntax where
<acronym>SQL</acronym> defines some string functions with a special syntax where
certain keywords rather than commas are used to separate the
arguments. Details are in <xref linkend="functions-string-sql">.
These functions are also implemented using the regular syntax for
@ -784,7 +784,7 @@
<para>
Additional string manipulation functions are available and are
listed below. Some of them are used internally to implement the
SQL string functions listed above.
<acronym>SQL</acronym> string functions listed above.
</para>
<table id="functions-string-other">
@ -1049,7 +1049,7 @@
<para>
The keyword <token>ILIKE</token> can be used instead of
<token>LIKE</token> to make the match case insensitive according
to the active locale. This is not in the SQL standard but is a
to the active locale. This is not in the <acronym>SQL</acronym> standard but is a
<productname>Postgres</productname> extension.
</para>
@ -1066,7 +1066,7 @@
<sect2 id="functions-regexp">
<title>POSIX Regular Expressions</title>
<title><acronym>POSIX</acronym> Regular Expressions</title>
<table>
<title>Regular Expression Match Operators</title>
@ -1106,7 +1106,7 @@
</table>
<para>
POSIX regular expressions provide a more powerful means for
<acronym>POSIX</acronym> regular expressions provide a more powerful means for
pattern matching than the <function>LIKE</function> function.
Many Unix tools such as <command>egrep</command>,
<command>sed</command>, or <command>awk</command> use a pattern
@ -1131,7 +1131,7 @@
<!-- derived from the re_format.7 man page -->
<para>
Regular expressions (<quote>RE</quote>s), as defined in POSIX
Regular expressions (<quote>RE</quote>s), as defined in <acronym>POSIX</acronym>
1003.2, come in two forms: modern REs (roughly those of
<command>egrep</command>; 1003.2 calls these
<quote>extended</quote> REs) and obsolete REs (roughly those of
@ -1379,7 +1379,7 @@
The <productname>Postgres</productname> formatting functions
provide a powerful set of tools for converting various data types
(date/time, integer, floating point, numeric) to formatted strings
and for converting from formatted strings to specific datetypes.
and for converting from formatted strings to specific data types.
These functions all follow a common calling convention: The first
argument is the value to be formatted and the second argument is a
template that defines the output format.
@ -1713,7 +1713,7 @@
<para>
A double quote (<quote><literal>"</literal></quote>) between
quotation marks is skipped and is not parsed. If you want to
have a double quote in the output you must preceed it with a
have a double quote in the output you must precede it with a
double backslash, for example <literal>'\\"YYYY
Month\\"'</literal>. <!-- " font-lock sanity :-) -->
</para>
@ -1829,7 +1829,7 @@
but to_char(-12, 'MI9999') produces <literal>'- 12'</literal>.
The Oracle implementation does not allow the use of
<literal>MI</literal> ahead of <literal>9</literal>, but rather
requires that <literal>9</literal> preceed
requires that <literal>9</literal> precede
<literal>MI</literal>.
</para>
</listitem>
@ -2027,125 +2027,648 @@
<title>Date/Time Functions</title>
<para>
The date/time functions provide a powerful set of tools
for manipulating various date/time types.
<xref linkend="functions-datetime-table"> shows the available
functions for date/time value processing. The basic arithmetic
operators (<literal>+</literal>, <literal>*</literal>, etc.) are
also available. For formatting functions, refer to <xref
linkend="functions-formatting">. You should be familiar with the
background information on date/time data types (see <xref
linkend="datatype-datetime">).
</para>
<para>
<table tocentry="1">
<table id="functions-datetime-table">
<title>Date/Time Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Name</entry>
<entry>Return Type</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry>abstime(timestamp)</entry>
<entry>abstime</entry>
<entry>convert to abstime</entry>
<entry>abstime(timestamp 'now')</entry>
</row>
<![IGNORE[
<!--
These two functions don't seem to do what it says here, or anything
reasonable at all for that matter.
-->
<row>
<entry>age(timestamp)</entry>
<entry>interval</entry>
<entry>preserve months and years</entry>
<entry>Subtract argument from current date, preserve years and months and days</entry>
<entry>age(timestamp '1957-06-13')</entry>
<entry>43 years 8 mons 3 days</entry>
</row>
<row>
<entry>age(timestamp,timestamp)</entry>
<entry>age(timestamp, timestamp)</entry>
<entry>interval</entry>
<entry>preserve months and years</entry>
<entry>age('now', timestamp '1957-06-13')</entry>
<entry></entry>
</row>
]]>
<row>
<entry>date_part(text,timestamp)</entry>
<entry>double precision</entry>
<entry>portion of date</entry>
<entry>date_part('dow',timestamp 'now')</entry>
<entry>current_date</entry>
<entry>date</entry>
<entry>
returns current date; see also <link
linkend="functions-datetime-current">below</link>
</entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry>date_part(text,interval)</entry>
<entry>double precision</entry>
<entry>portion of time</entry>
<entry>date_part('hour',interval '4 hrs 3 mins')</entry>
<entry>current_time</entry>
<entry>time</entry>
<entry>
returns current time (of day); see also <link
linkend="functions-datetime-current">below</link>
</entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry>date_trunc(text,timestamp)</entry>
<entry>current_timestamp</entry>
<entry>timestamp</entry>
<entry>truncate date</entry>
<entry>date_trunc('month',abstime 'now')</entry>
<entry>
returns current date and time; see also <link
linkend="functions-datetime-current">below</link>
</entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry>interval(reltime)</entry>
<entry>interval</entry>
<entry>convert to interval</entry>
<entry>interval(reltime '4 hours')</entry>
<entry>date_part(text, timestamp)</entry>
<entry>double precision</entry>
<entry>
extract subfield from date/time value (equivalent to
<function>extract</function>); see also <link
linkend="functions-datetime-datepart">below</link>
</entry>
<entry>date_part('hour', timestamp '2001-02-16 20:38:40')</entry>
<entry>20</entry>
</row>
<row>
<entry>date_part(text, interval)</entry>
<entry>double precision</entry>
<entry>
extract subfield from interval value (equivalent to
<function>extract</function>); see also <link
linkend="functions-datetime-datepart">below</link>
</entry>
<entry>date_part('month', interval '2 years 3 months')</entry>
<entry>3</entry>
</row>
<row>
<entry>date_trunc(text, timestamp)</entry>
<entry>timestamp</entry>
<entry>
truncate date to specified precision; see also <link
linkend="functions-datetime-trunc">below</link>
</entry>
<entry>date_trunc('hour', timestamp '2001-02-16 20:38:40')</entry>
<entry>2001-02-16 20:00:00+00</entry>
</row>
<row>
<entry>extract(identifier from timestamp)</entry>
<entry>double precision</entry>
<entry>
extract subfield from date/time value; see also <link
linkend="functions-datetime-extract">below</link>
</entry>
<entry>extract(hour from timestamp '2001-02-16 20:38:40')</entry>
<entry>20</entry>
</row>
<row>
<entry>extract(identifier from interval)</entry>
<entry>double precision</entry>
<entry>
extract subfield from interval value; see also <link
linkend="functions-datetime-extract">below</link>
</entry>
<entry>extract(month from interval '2 years 3 months')</entry>
<entry>3</entry>
</row>
<row>
<entry>isfinite(timestamp)</entry>
<entry>bool</entry>
<entry>a finite time?</entry>
<entry>isfinite(timestamp 'now')</entry>
<entry>boolean</entry>
<entry>Returns true if the time stamp is finite (neither invalid nor infinity)</entry>
<entry>isfinite(timestamp '2001-02-16 21:28:30')</entry>
<entry>true</entry>
</row>
<row>
<entry>isfinite(interval)</entry>
<entry>bool</entry>
<entry>a finite time?</entry>
<entry>isfinite(interval '4 hrs')</entry>
<entry>boolean</entry>
<entry>Returns true if the interval is finite in length</entry>
<entry>isfinite(interval '4 hours')</entry>
<entry>true</entry>
</row>
<row>
<entry>reltime(interval)</entry>
<entry>reltime</entry>
<entry>convert to reltime</entry>
<entry>reltime(interval '4 hrs')</entry>
<entry>now()</entry>
<entry>timestamp</entry>
<entry>
returns current date and time (equivalent to
<function>current_timestamp</function>); see also <link
linkend="functions-datetime-current">below</link>
</entry>
<entry></entry>
<entry></entry>
</row>
<row>
<entry>timestamp(date)</entry>
<entry>timestamp</entry>
<entry>convert to timestamp</entry>
<entry>timestamp(date 'today')</entry>
<entry>convert date to timestamp</entry>
<entry>timestamp(date '2000-12-25')</entry>
<entry>2000-12-25 00:00:00</entry>
</row>
<row>
<entry>timestamp(date,time)</entry>
<entry>timestamp(date, time)</entry>
<entry>timestamp</entry>
<entry>convert to timestamp</entry>
<entry>timestamp(timestamp '1998-02-24',time '23:07');</entry>
</row>
<row>
<entry>to_char(timestamp,text)</entry>
<entry>text</entry>
<entry>convert to string</entry>
<entry>to_char(timestamp '1998-02-24','DD');</entry>
<entry>combine date and time into a timestamp</entry>
<entry>timestamp(date '1998-02-24',time '23:07')</entry>
<entry>1998-02-24 23:07:00</entry>
</row>
</tbody>
</tgroup>
</table>
<sect2 id="functions-datetime-extract">
<title><function>EXTRACT</function>, <function>date_part</function></title>
<synopsis>
EXTRACT (<replaceable>field</replaceable> FROM <replaceable>source</replaceable>)
</synopsis>
<para>
The <function>extract</function> function retrieves sub-fields
from date/time values, such as year or hour.
<replaceable>source</replaceable> is a value expression that
evaluates to type <type>timestamp</type> or <type>interval</type>.
(Expressions of type <type>date</type> or <type>time</type> will
be cast to <type>timestamp</type> and can therefore be used as
well.) <replaceable>field</replaceable> is an identifier (not a
string!) that selects what field to extract from the source value.
The <function>extract</function> function returns values of type
<type>double precision</type>.
The following are valid values:
<!-- alphabetical -->
<variablelist>
<varlistentry>
<term>century</term>
<listitem>
<para>
The year field divided by 100
</para>
<informalexample>
<screen>
SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>20</computeroutput>
</screen>
</informalexample>
<para>
Note that this is not really the century that the date is in.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>day</term>
<listitem>
<para>
The day (of the month) field (1 - 31)
</para>
<informalexample>
<screen>
SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>16</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>decade</term>
<listitem>
<para>
The year field divided by 10
</para>
<informalexample>
<screen>
SELECT EXTRACT(DECADE FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>200</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>dow</term>
<listitem>
<para>
The day of the week (0 - 6; Sunday is 0) (for
<type>timestamp</type> values only)
</para>
<informalexample>
<screen>
SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>5</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>doy</term>
<listitem>
<para>
The day of the year (1 - 365/366) (for <type>timestamp</type> values only)
</para>
<informalexample>
<screen>
SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>47</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>epoch</term>
<listitem>
<para>
For <type>date</type> and <type>timestamp</type> values, the
number of seconds since 1970-01-01 00:00:00 (Result may be
negative.); for <type>interval</type> values, the total number
of seconds in the interval
</para>
<informalexample>
<screen>
SELECT EXTRACT(EPOCH FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>982352320</computeroutput>
SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
<lineannotation>Result: </lineannotation><computeroutput>442800</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>hour</term>
<listitem>
<para>
The hour field (0 - 23)
</para>
<informalexample>
<screen>
SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>20</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>microseconds</term>
<listitem>
<para>
The seconds field, including fractional parts, multiplied by 1
000 000. Note that this includes full seconds.
</para>
<informalexample>
<screen>
SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5');
<lineannotation>Result: </lineannotation><computeroutput>28500000</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>millennium</term>
<listitem>
<para>
The year field divided by 1000
</para>
<informalexample>
<screen>
SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2</computeroutput>
</screen>
</informalexample>
<para>
Note that this is not really the millennium that the date is in.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>milliseconds</term>
<listitem>
<para>
The seconds field, including fractional parts, multiplied by
1000. Note that this includes full seconds.
</para>
<informalexample>
<screen>
SELECT EXTRACT(MILLISECONDS FROM TIME '17:12:28.5');
<lineannotation>Result: </lineannotation><computeroutput>28500</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>minute</term>
<listitem>
<para>
The minutes field (0 - 59)
</para>
<informalexample>
<screen>
SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>38</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>month</term>
<listitem>
<para>
For <type>timestamp</type> values, the number of the month
within the year (1 - 12) ; for <type>interval</type> values
the number of months, modulo 12 (0 - 11)
</para>
<informalexample>
<screen>
SELECT EXTRACT(MONTH FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2</computeroutput>
SELECT EXTRACT(MONTH FROM INTERVAL '2 years 3 months');
<lineannotation>Result: </lineannotation><computeroutput>3</computeroutput>
SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months');
<lineannotation>Result: </lineannotation><computeroutput>1</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>quarter</term>
<listitem>
<para>
The quarter of the year (1 - 4) that the day is in (for
<type>timestamp</type> values only)
</para>
<informalexample>
<screen>
SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>1</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>second</term>
<listitem>
<para>
The seconds field, including fractional parts (0 -
59<footnote><simpara>60 if leap seconds are
implemented by the operating system</simpara></footnote>)
</para>
<informalexample>
<screen>
SELECT EXTRACT(SECOND FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>40</computeroutput>
SELECT EXTRACT(SECOND FROM TIME '17:12:28.5');
<lineannotation>Result: </lineannotation><computeroutput>28.5</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>week</term>
<listitem>
<para>
From a <type>timestamp</type> value, calculate the number of
the week of the year that the day is in. By definition
(<acronym>ISO</acronym> 8601), the first week of a year
contains January 4 of that year. (The <acronym>ISO</acronym>
week starts on Monday.) In other words, the first Thursday of
a year is in week 1 of that year.
</para>
<informalexample>
<screen>
SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>7</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<varlistentry>
<term>year</term>
<listitem>
<para>
The year field
</para>
<informalexample>
<screen>
SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2001</computeroutput>
</screen>
</informalexample>
</listitem>
</varlistentry>
<!--
tz
tz_hour
tz_minute
-->
</variablelist>
</para>
<para>
For the
<function>date_part</function> and <function>date_trunc</function>
functions, arguments can be
`<literal>year</literal>', `<literal>month</literal>',
`<literal>day</literal>', `<literal>hour</literal>',
`<literal>minute</literal>', and `<literal>second</literal>',
as well as the more specialized quantities
`<literal>decade</literal>', `<literal>century</literal>',
`<literal>millennium</literal>', `<literal>millisecond</literal>',
and `<literal>microsecond</literal>'.
<function>date_part</function> allows `<literal>dow</literal>'
to return day of week, '<literal>week</literal>' to return the
ISO-defined week of year, and `<literal>epoch</literal>' to return
seconds since 1970 (for <type>timestamp</type>)
or '<literal>epoch</literal>' to return total elapsed seconds
(for <type>interval</type>).
The <function>extract</function> function is primarily intended
for computational processing. For formatting date/time values for
display, see <xref linkend="functions-formatting">.
</para>
</sect1>
<anchor id="functions-datetime-datepart">
<para>
The <function>date_part</function> function is the traditional
<productname>Postgres</productname> equivalent to the
<acronym>SQL</acronym>-function <function>extract</function>:
<synopsis>
date_part('<replaceable>field</replaceable>', <replaceable>source</replaceable>)
</synopsis>
Note that here the <replaceable>field</replaceable> value needs to
be a string. The valid field values for
<function>date_part</function> are the same as for
<function>extract</function>.
</para>
<informalexample>
<screen>
SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>16</computeroutput>
SELECT date_part('hour', INTERVAL '4 hours 3 minutes')
<lineannotation>Result: </lineannotation><computeroutput>4</computeroutput>
</screen>
</informalexample>
</sect2>
<sect2 id="functions-datetime-trunc">
<title><function>date_trunc</function></title>
<para>
The function <function>date_trunc</function> is conceptually
similar to the <function>trunc</function> function for numbers.
</para>
<para>
<synopsis>
date_trunc('<replaceable>field</replaceable>', <replaceable>source</replaceable>)
</synopsis>
<replaceable>source</replaceable> is a value expression of type
<type>timestamp</type> (values of type <type>date</type> and
<type>time</type> are cast automatically).
<replaceable>field</replaceable> selects to which precision to
truncate the time stamp value. The return value is of type
<type>timestamp</type> with all fields that are less than the
selected one set to zero (or one, for day and month).
</para>
<para>
Valid values for <replaceable>field</replaceable> are:
<simplelist>
<member>microseconds</member>
<member>milliseconds</member>
<member>second</member>
<member>minute</member>
<member>hour</member>
<member>day</member>
<member>month</member>
<member>year</member>
<member>decade</member>
<member>century</member>
<member>millennium</member>
</simplelist>
</para>
<informalexample>
<para>
<screen>
SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 20:00:00+00</computeroutput>
SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2001-01-01 00:00:00+00</computeroutput>
</screen>
</para>
</informalexample>
</sect2>
<sect2 id="functions-datetime-current">
<title>Current Date/Time</title>
<para>
The following functions are available to select the current date and/or time:
<synopsis>
CURRENT_TIME
CURRENT_DATE
CURRENT_TIMESTAMP
</synopsis>
Note that because of the requirements of the
<acronym>SQL</acronym> standard, these functions must not be
called with trailing parentheses.
</para>
<informalexample>
<screen>
SELECT CURRENT_TIME;
<computeroutput>19:07:13</computeroutput>
SELECT CURRENT_DATE;
<computeroutput>2001-02-17</computeroutput>
SELECT CURRENT_TIMESTAMP;
<computeroutput>2001-02-17 19:07:32+00</computeroutput>
</screen>
</informalexample>
<para>
The function <function>now()</function> is the traditional
<productname>Postgres</productname> equivalent to
<function>CURRENT_TIMESTAMP</function>.
<productname>Postgres</productname> furthermore has special
date/time <quote>constants</quote> that can be used to specify the
current time. The following three all return the same result:
<programlisting>
SELECT CURRENT_TIMESTAMP;
SELECT now();
SELECT TIMESTAMP 'now';
</programlisting>
<note>
<para>
You do not want to use the third form when specifying a DEFAULT
value when creating a table. The system will immediately
evaluate the constant, thus 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.
</para>
</note>
</para>
</sect2>
</sect1>
<sect1 id="functions-geometry">
@ -2335,13 +2858,13 @@
</row>
<row>
<entry>isclosed(path)</entry>
<entry>bool</entry>
<entry>boolean</entry>
<entry>a closed path?</entry>
<entry>isclosed(path '((0,0),(1,1),(2,0))')</entry>
</row>
<row>
<entry>isopen(path)</entry>
<entry>bool</entry>
<entry>boolean</entry>
<entry>an open path?</entry>
<entry>isopen(path '[(0,0),(1,1),(2,0)]')</entry>
</row>
@ -2704,7 +3227,7 @@ Not defined by this name. Implements the intersection operator '#'
<title>Conditional Expressions</title>
<para>
This section descibes the SQL-compliant conditional expressions
This section describes the <acronym>SQL</acronym>-compliant conditional expressions
available in <productname>Postgres</productname>.
</para>
@ -2728,9 +3251,9 @@ END
<para>
The <acronym>SQL</acronym> <token>CASE</token> expression is a
generic conditional expression, similar to if/else statements in
other languages. <token>CASE</token> clauses can be used whereever
other languages. <token>CASE</token> clauses can be used wherever
an expression is valid. <replaceable>condition</replaceable> is an
expression that returns a boolean result. If the result is true
expression that returns a <type>boolean</type> result. If the result is true
then the value of the <token>CASE</token> expression is
<replaceable>result</replaceable>. If the result is false any
subsequent <token>WHEN</token> clauses are searched in the same