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postgres/doc/src/sgml/func.sgml
Thomas G. Lockhart fe2f878173 Fix (mis)information about NULLIF() SQL function. 
Thanks to Tom Lane for pointing it out.
1999-09-29 05:20:20 +00:00

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<chapter id="functions">
<title id="functions-title">Functions</title>
<abstract>
<para>
Describes the built-in functions available
in <productname>Postgres</productname>.
</para>
</abstract>
<para>
Many data types have functions available for conversion to other related types.
In addition, there are some type-specific functions. Some functions are also
available through operators and may be documented as operators only.
</para>
<sect1>
<title id="sql-funcs">SQL Functions</title>
<para>
<quote><acronym>SQL</acronym> functions</quote> are constructs
defined by the <acronym>SQL92</acronym> standard which have
function-like syntax but which can not be implemented as simple
functions.
</para>
<para>
<table tocentry="1">
<title>SQL Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry> COALESCE(<replaceable class="parameter">list</replaceable>) </entry>
<entry> non-NULL </entry>
<entry> return first non-NULL value in list </entry>
<entry> COALESCE(<replaceable class="parameter">r"</replaceable>le>, <replaceable
class="parameter">c2</replaceable> + 5, 0) </entry>
</row>
<row>
<entry> NULLIF(<replaceable class="parameter">input</replaceable>,<replaceable class="parameter">value</replaceable>) </entry>
<entry> <replaceable class="parameter">input</replaceable> or NULL </entry>
<entry> return NULL if <replaceable class="parameter">input</replaceable> = <replaceable class="parameter">value</replaceable> </entry>
<entry> NULLIF(<replaceable class="parameter">c1</replaceable>, 'N/A')</entry>
</row>
<row>
<entry> CASE WHEN <replaceable class="parameter">expr</replaceable> THEN <replaceable class="parameter">expr</replaceable> [...] ELSE <replaceable class="parameter">expr</replaceable> END </entry>
<entry> <replaceable class="parameter">expr</replaceable> </entry>
<entry> return expression for first true clause </entry>
<entry> CASE WHEN <replaceable class="parameter">c1</replaceable> = 1 THEN 'match' ELSE 'no match' END </entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</sect1>
<sect1>
<title id="math-funcs">Mathematical Functions</title>
<para>
<table tocentry="1">
<title>Mathematical Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry> dexp(float8) </entry>
<entry> float8 </entry>
<entry> raise e to the specified exponent </entry>
<entry> dexp(2.0) </entry>
</row>
<row>
<entry> dpow(float8,float8) </entry>
<entry> float8 </entry>
<entry> raise a number to the specified exponent </entry>
<entry> dpow(2.0, 16.0) </entry>
</row>
<row>
<entry> float(int) </entry>
<entry> float8 </entry>
<entry> convert integer to floating point </entry>
<entry> float(2) </entry>
</row>
<row>
<entry> float4(int) </entry>
<entry> float4 </entry>
<entry> convert integer to floating point </entry>
<entry> float4(2) </entry>
</row>
<row>
<entry> integer(float) </entry>
<entry> int </entry>
<entry> convert floating point to integer </entry>
<entry> integer(2.0) </entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</sect1>
<sect1>
<title>String Functions</title>
<para>
SQL92 defines string functions with specific syntax. Some of these
are implemented using other <productname>Postgres</productname> functions.
The supported string types for <acronym>SQL92</acronym> are
<type>char</type>, <type>varchar</type>, and <type>text</type>.
</para>
<para>
<table tocentry="1">
<title><acronym>SQL92</acronym> String Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry> char_length(string) </entry>
<entry> int4 </entry>
<entry> length of string </entry>
<entry> char_length('jose') </entry>
</row>
<row>
<entry> character_length(string) </entry>
<entry> int4 </entry>
<entry> length of string </entry>
<entry> char_length('jose') </entry>
</row>
<row>
<entry> lower(string) </entry>
<entry> string </entry>
<entry> convert string to lower case </entry>
<entry> lower('TOM') </entry>
</row>
<row>
<entry> octet_length(string) </entry>
<entry> int4 </entry>
<entry> storage length of string </entry>
<entry> octet_length('jose') </entry>
</row>
<row>
<entry> position(string in string) </entry>
<entry> int4 </entry>
<entry> location of specified substring </entry>
<entry> position('o' in 'Tom') </entry>
</row>
<row>
<entry> substring(string [from int] [for int]) </entry>
<entry> string </entry>
<entry> extract specified substring </entry>
<entry> substring('Tom' from 2 for 2) </entry>
</row>
<row>
<entry> trim([leading|trailing|both] [string] from string) </entry>
<entry> string </entry>
<entry> trim characters from string </entry>
<entry> trim(both 'x' from 'xTomx') </entry>
</row>
<row>
<entry> upper(text) </entry>
<entry> text </entry>
<entry> convert text to upper case </entry>
<entry> upper('tom') </entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
Many additional string functions are available for text, varchar(), and char() types.
Some are used internally to implement the SQL92 string functions listed above.
</para>
<para>
<table tocentry="1">
<title>String Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry> char(text) </entry>
<entry> char </entry>
<entry> convert text to char type </entry>
<entry> char('text string') </entry>
</row>
<row>
<entry> char(varchar) </entry>
<entry> char </entry>
<entry> convert varchar to char type </entry>
<entry> char(varchar 'varchar string') </entry>
</row>
<row>
<entry> initcap(text) </entry>
<entry> text </entry>
<entry> first letter of each word to upper case </entry>
<entry> initcap('thomas') </entry>
</row>
<row>
<entry> lpad(text,int,text) </entry>
<entry> text </entry>
<entry> left pad string to specified length </entry>
<entry> lpad('hi',4,'??') </entry>
</row>
<row>
<entry> ltrim(text,text) </entry>
<entry> text </entry>
<entry> left trim characters from text </entry>
<entry> ltrim('xxxxtrim','x') </entry>
</row>
<row>
<entry> textpos(text,text) </entry>
<entry> text </entry>
<entry> locate specified substring </entry>
<entry> position('high','ig') </entry>
</row>
<row>
<entry> rpad(text,int,text) </entry>
<entry> text </entry>
<entry> right pad string to specified length </entry>
<entry> rpad('hi',4,'x') </entry>
</row>
<row>
<entry> rtrim(text,text) </entry>
<entry> text </entry>
<entry> right trim characters from text </entry>
<entry> rtrim('trimxxxx','x') </entry>
</row>
<row>
<entry> substr(text,int[,int]) </entry>
<entry> text </entry>
<entry> extract specified substring </entry>
<entry> substr('hi there',3,5) </entry>
</row>
<row>
<entry> text(char) </entry>
<entry> text </entry>
<entry> convert char to text type </entry>
<entry> text('char string') </entry>
</row>
<row>
<entry> text(varchar) </entry>
<entry> text </entry>
<entry> convert varchar to text type </entry>
<entry> text(varchar 'varchar string') </entry>
</row>
<row>
<entry> translate(text,from,to) </entry>
<entry> text </entry>
<entry> convert character in string </entry>
<entry> translate('12345', '1', 'a') </entry>
</row>
<row>
<entry> varchar(char) </entry>
<entry> varchar </entry>
<entry> convert char to varchar type </entry>
<entry> varchar('char string') </entry>
</row>
<row>
<entry> varchar(text) </entry>
<entry> varchar </entry>
<entry> convert text to varchar type </entry>
<entry> varchar('text string') </entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
Most functions explicitly defined for text will work for char() and varchar() arguments.
</para>
</sect1>
<sect1>
<title>Date/Time Functions</title>
<para>
The date/time functions provide a powerful set of tools
for manipulating various date/time types.
</para>
<para>
<table tocentry="1">
<title>Date/Time Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry> abstime(datetime) </entry>
<entry> abstime </entry>
<entry> convert to abstime </entry>
<entry> abstime('now'::datetime) </entry>
</row>
<row>
<entry> age(datetime,datetime) </entry>
<entry> timespan </entry>
<entry> preserve months and years </entry>
<entry> age('now','1957-06-13'::datetime) </entry>
</row>
<row>
<entry> datetime(abstime) </entry>
<entry> datetime </entry>
<entry> convert to datetime </entry>
<entry> datetime('now'::abstime) </entry>
</row>
<row>
<entry> datetime(date) </entry>
<entry> datetime </entry>
<entry> convert to datetime </entry>
<entry> datetime('today'::date) </entry>
</row>
<row>
<entry> datetime(date,time) </entry>
<entry> datetime </entry>
<entry> convert to datetime </entry>
<entry> datetime('1998-02-24'::datetime, '23:07'::time); </entry>
</row>
<row>
<entry> date_part(text,datetime) </entry>
<entry> float8 </entry>
<entry> portion of date </entry>
<entry> date_part('dow','now'::datetime) </entry>
</row>
<row>
<entry> date_part(text,timespan) </entry>
<entry> float8 </entry>
<entry> portion of time </entry>
<entry> date_part('hour','4 hrs 3 mins'::timespan) </entry>
</row>
<row>
<entry> date_trunc(text,datetime) </entry>
<entry> datetime </entry>
<entry> truncate date </entry>
<entry> date_trunc('month','now'::abstime) </entry>
</row>
<row>
<entry> isfinite(abstime) </entry>
<entry> bool </entry>
<entry> a finite time? </entry>
<entry> isfinite('now'::abstime) </entry>
</row>
<row>
<entry> isfinite(datetime) </entry>
<entry> bool </entry>
<entry> a finite time? </entry>
<entry> isfinite('now'::datetime) </entry>
</row>
<row>
<entry> isfinite(timespan) </entry>
<entry> bool </entry>
<entry> a finite time? </entry>
<entry> isfinite('4 hrs'::timespan) </entry>
</row>
<row>
<entry> reltime(timespan) </entry>
<entry> reltime </entry>
<entry> convert to reltime </entry>
<entry> reltime('4 hrs'::timespan) </entry>
</row>
<row>
<entry> timespan(reltime) </entry>
<entry> timespan </entry>
<entry> convert to timespan </entry>
<entry> timespan('4 hours'::reltime) </entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
For the
<function>date_part</function> and <function>date_trunc</function>
functions, arguments can be
`year', `month', `day', `hour', `minute', and `second',
as well as the more specialized quantities
`decade', `century', `millenium', `millisecond', and `microsecond'.
<function>date_part</function> allows `dow'
to return day of week and `epoch' to return seconds since 1970
(for <type>datetime</type>)
or 'epoch' to return total elapsed seconds (for <type>timespan</type>).
</para>
</sect1>
<sect1>
<title>Geometric Functions</title>
<para>
The geometric types point, box, lseg, line, path, polygon, and
circle have a large set of native support functions.
</para>
<para>
<table tocentry="1">
<title>Geometric Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry> area(box) </entry>
<entry> float8 </entry>
<entry> area of box </entry>
<entry> area('((0,0),(1,1))'::box) </entry>
</row>
<row>
<entry> area(circle) </entry>
<entry> float8 </entry>
<entry> area of circle </entry>
<entry> area('((0,0),2.0)'::circle) </entry>
</row>
<row>
<entry> box(box,box) </entry>
<entry> box </entry>
<entry> boxes to intersection box </entry>
<entry> box('((0,0),(1,1))','((0.5,0.5),(2,2))') </entry>
</row>
<row>
<entry> center(box) </entry>
<entry> point </entry>
<entry> center of object </entry>
<entry> center('((0,0),(1,2))'::box) </entry>
</row>
<row>
<entry> center(circle) </entry>
<entry> point </entry>
<entry> center of object </entry>
<entry> center('((0,0),2.0)'::circle) </entry>
</row>
<row>
<entry> diameter(circle) </entry>
<entry> float8 </entry>
<entry> diameter of circle </entry>
<entry> diameter('((0,0),2.0)'::circle) </entry>
</row>
<row>
<entry> height(box) </entry>
<entry> float8 </entry>
<entry> vertical size of box </entry>
<entry> height('((0,0),(1,1))'::box) </entry>
</row>
<row>
<entry> isclosed(path) </entry>
<entry> bool </entry>
<entry> a closed path? </entry>
<entry> isclosed('((0,0),(1,1),(2,0))'::path) </entry>
</row>
<row>
<entry> isopen(path) </entry>
<entry> bool </entry>
<entry> an open path? </entry>
<entry> isopen('[(0,0),(1,1),(2,0)]'::path) </entry>
</row>
<row>
<entry> length(lseg) </entry>
<entry> float8 </entry>
<entry> length of line segment </entry>
<entry> length('((-1,0),(1,0))'::lseg) </entry>
</row>
<row>
<entry> length(path) </entry>
<entry> float8 </entry>
<entry> length of path </entry>
<entry> length('((0,0),(1,1),(2,0))'::path) </entry>
</row>
<row>
<entry> pclose(path) </entry>
<entry> path </entry>
<entry> convert path to closed </entry>
<entry> popen('[(0,0),(1,1),(2,0)]'::path) </entry>
</row>
<row>
<entry> point(lseg,lseg) </entry>
<entry> point </entry>
<entry> intersection </entry>
<entry> point('((-1,0),(1,0))'::lseg,'((-2,-2),(2,2))'::lseg) </entry>
</row>
<row>
<entry> points(path) </entry>
<entry> int4 </entry>
<entry> number of points </entry>
<entry> points('[(0,0),(1,1),(2,0)]'::path) </entry>
</row>
<row>
<entry> popen(path) </entry>
<entry> path </entry>
<entry> convert path to open </entry>
<entry> popen('((0,0),(1,1),(2,0))'::path) </entry>
</row>
<row>
<entry> radius(circle) </entry>
<entry> float8 </entry>
<entry> radius of circle </entry>
<entry> radius('((0,0),2.0)'::circle) </entry>
</row>
<row>
<entry> width(box) </entry>
<entry> float8 </entry>
<entry> horizontal size </entry>
<entry> width('((0,0),(1,1))'::box) </entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
<table tocentry="1">
<title>Geometric Type Conversion Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry> box(circle) </entry>
<entry> box </entry>
<entry> convert circle to box </entry>
<entry> box('((0,0),2.0)'::circle) </entry>
</row>
<row>
<entry> box(point,point) </entry>
<entry> box </entry>
<entry> convert points to box </entry>
<entry> box('(0,0)'::point,'(1,1)'::point) </entry>
</row>
<row>
<entry> box(polygon) </entry>
<entry> box </entry>
<entry> convert polygon to box </entry>
<entry> box('((0,0),(1,1),(2,0))'::polygon) </entry>
</row>
<row>
<entry> circle(box) </entry>
<entry> circle </entry>
<entry> convert to circle </entry>
<entry> circle('((0,0),(1,1))'::box) </entry>
</row>
<row>
<entry> circle(point,float8) </entry>
<entry> circle </entry>
<entry> convert to circle </entry>
<entry> circle('(0,0)'::point,2.0) </entry>
</row>
<row>
<entry> lseg(box) </entry>
<entry> lseg </entry>
<entry> convert diagonal to lseg </entry>
<entry> lseg('((-1,0),(1,0))'::box) </entry>
</row>
<row>
<entry> lseg(point,point) </entry>
<entry> lseg </entry>
<entry> convert to lseg </entry>
<entry> lseg('(-1,0)'::point,'(1,0)'::point) </entry>
</row>
<row>
<entry> path(polygon) </entry>
<entry> point </entry>
<entry> convert to path </entry>
<entry> path('((0,0),(1,1),(2,0))'::polygon) </entry>
</row>
<row>
<entry> point(circle) </entry>
<entry> point </entry>
<entry> convert to point (center) </entry>
<entry> point('((0,0),2.0)'::circle) </entry>
</row>
<row>
<entry> point(lseg,lseg) </entry>
<entry> point </entry>
<entry> convert to point (intersection) </entry>
<entry> point('((-1,0),(1,0))'::lseg, '((-2,-2),(2,2))'::lseg) </entry>
</row>
<row>
<entry> point(polygon) </entry>
<entry> point </entry>
<entry> center of polygon </entry>
<entry> point('((0,0),(1,1),(2,0))'::polygon) </entry>
</row>
<row>
<entry> polygon(box) </entry>
<entry> polygon </entry>
<entry> convert to polygon with 12 points </entry>
<entry> polygon('((0,0),(1,1))'::box) </entry>
</row>
<row>
<entry> polygon(circle) </entry>
<entry> polygon </entry>
<entry> convert to 12-point polygon </entry>
<entry> polygon('((0,0),2.0)'::circle) </entry>
</row>
<row>
<entry> polygon(<replaceable class="parameter">npts</replaceable>,circle) </entry>
<entry> polygon </entry>
<entry> convert to <replaceable class="parameter">npts</replaceable> polygon </entry>
<entry> polygon(12,'((0,0),2.0)'::circle) </entry>
</row>
<row>
<entry> polygon(path) </entry>
<entry> polygon </entry>
<entry> convert to polygon </entry>
<entry> polygon('((0,0),(1,1),(2,0))'::path) </entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
<table tocentry="1">
<title>Geometric Upgrade Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry> isoldpath(path) </entry>
<entry> path </entry>
<entry> test path for pre-v6.1 form </entry>
<entry> isoldpath('(1,3,0,0,1,1,2,0)'::path) </entry>
</row>
<row>
<entry> revertpoly(polygon) </entry>
<entry> polygon </entry>
<entry> convert pre-v6.1 polygon </entry>
<entry> revertpoly('((0,0),(1,1),(2,0))'::polygon) </entry>
</row>
<row>
<entry> upgradepath(path) </entry>
<entry> path </entry>
<entry> convert pre-v6.1 path </entry>
<entry> upgradepath('(1,3,0,0,1,1,2,0)'::path) </entry>
</row>
<row>
<entry> upgradepoly(polygon) </entry>
<entry> polygon </entry>
<entry> convert pre-v6.1 polygon </entry>
<entry> upgradepoly('(0,1,2,0,1,0)'::polygon) </entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</sect1>
<sect1>
<title id="cidr-funcs">IP V4 Functions</title>
<para>
<table tocentry="1">
<title><productname>Postgres</productname>IP V4 Functions</title>
<tgroup cols="4">
<thead>
<row>
<entry>Function</entry>
<entry>Returns</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry> broadcast(cidr) </entry>
<entry> text </entry>
<entry> construct broadcast address as text </entry>
<entry> broadcast('192.168.1.5/24') </entry>
</row>
<row>
<entry> broadcast(inet) </entry>
<entry> text </entry>
<entry> construct broadcast address as text </entry>
<entry> broadcast('192.168.1.5/24') </entry>
</row>
<row>
<entry> host(inet) </entry>
<entry> text </entry>
<entry> extract host address as text </entry>
<entry> host('192.168.1.5/24') </entry>
</row>
<row>
<entry> masklen(cidr) </entry>
<entry> int4 </entry>
<entry> calculate netmask length </entry>
<entry> masklen('192.168.1.5/24') </entry>
</row>
<row>
<entry> masklen(inet) </entry>
<entry> int4 </entry>
<entry> calculate netmask length </entry>
<entry> masklen('192.168.1.5/24') </entry>
</row>
<row>
<entry> netmask(inet) </entry>
<entry> text </entry>
<entry> construct netmask as text </entry>
<entry> netmask('192.168.1.5/24') </entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</sect1>
</chapter>
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