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Split function and operator User Guide info 

from datatype.sgml into separate files.
Add type conversion information.
Format historical release notes.
This commit is contained in:
Thomas G. Lockhart 1998-07-08 13:53:15 +00:00
parent febe53d813
commit ba3a99f193
8 changed files with 3436 additions and 833 deletions
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doc/src/sgml/datatype.sgml
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@ -190,26 +190,38 @@ several possibilities for formats, such as date and time types.
<Para>
<ProductName>Postgres</ProductName> has features at the forefront of ORDBMS development. In addition to
SQL3 conformance, substantial portions of SQL92 are also supported.
Although we strive for SQL92 compliance, there are some cases in the standard
Although we strive for SQL92 compliance, there are some aspects of the standard
which are ill considered and which should not live through subsequent standards.
<ProductName>Postgres</ProductName> will not make great efforts to conform to these cases. However, these
cases tend to be little-used and obsure, and a typical user is not likely to
<ProductName>Postgres</ProductName> will not make great efforts to conform to these aspects;
however, these
tend to apply in little-used or obsure cases, and a typical user is not likely to
run into them.
<Para>
Although most of the input and output functions corresponding to the
Most of the input and output functions corresponding to the
base types (e.g., integers and floating point numbers) do some
error-checking, some are not particularly rigorous about it. More
importantly, few of the operators and functions (e.g.,
addition and multiplication) perform any error-checking at all.
Consequently, many of the numeric operators can (for example)
error-checking.
Some of the operators and functions (e.g.,
addition and multiplication) do not perform run-time error-checking in the
interests of improving execution speed.
On some systems, for example, the numeric operators for some data types may
silently underflow or overflow.
</Para>
<Para>
Some of the input and output functions are not invertible. That is,
Note that some of the input and output functions are not invertible. That is,
the result of an output function may lose precision when compared to
the original input.
<note>
<para>
The original <ProductName>Postgres</ProductName> v4.2 code received from
Berkeley rounded all double precision floating point results to six digits for
output. Starting with v6.1, floating point numbers are allowed to retain
most of the intrinsic precision of the type (typically 15 digits for doubles, 6 digits
for 4-byte floats). Other types with underlying floating point fields (e.g. geometric
types) carry similar precision.
</note>
</Para>
<Sect1>
@ -245,17 +257,23 @@ floating point numbers.
<ENTRY>Usual choice for fixed-precision</ENTRY>
<ENTRY>-2147483648 to +2147483647</ENTRY>
</ROW>
<ROW>
<ENTRY>int8</ENTRY>
<ENTRY>8 bytes</ENTRY>
<ENTRY>Very large range fixed-precision</ENTRY>
<ENTRY>+/- &gt; 18 decimal places</ENTRY>
</ROW>
<ROW>
<ENTRY>float4</ENTRY>
<ENTRY>4 bytes</ENTRY>
<ENTRY>Variable-precision</ENTRY>
<ENTRY>7 decimal places</ENTRY>
<ENTRY>6 decimal places</ENTRY>
</ROW>
<ROW>
<ENTRY>float8</ENTRY>
<ENTRY>8 bytes</ENTRY>
<ENTRY>Variable-precision</ENTRY>
<ENTRY>14 decimal places</ENTRY>
<ENTRY>15 decimal places</ENTRY>
</ROW>
</TBODY>
</TGROUP>
@ -266,6 +284,7 @@ floating point numbers.
The <FirstTerm>exact numerics</FirstTerm> <Type>decimal</Type> and <Type>numeric</Type>
have fully implemented syntax but currently (<ProductName>Postgres</ProductName> v6.3)
support only a small range of precision and/or range values.
The <type>int8</type> type may not be available on all platforms.
</Para>
</Sect1>
@ -1267,790 +1286,3 @@ Circles are output using the first syntax.
</Sect1>
<Chapter>
<Title>Operators</Title>
<Para>
<ProductName>Postgres</ProductName> provides a large number of built-in operators on system types.
These operators are declared in the system catalog
pg_operator. Every entry in pg_operator includes
the name of the procedure that implements the operator and the
class <Acronym>OIDs</Acronym> of the input and output types.
<Para>
To view all variations of the <Quote>||</Quote> string concatenation operator, try
<ProgramListing>
SELECT oprleft, oprright, oprresult, oprcode
FROM pg_operator WHERE oprname = '||';
oprleft|oprright|oprresult|oprcode
-------+--------+---------+-------
25| 25| 25|textcat
1042| 1042| 1042|textcat
1043| 1043| 1043|textcat
(3 rows)
</ProgramListing>
</Para>
<Para>
<TABLE TOCENTRY="1">
<TITLE><ProductName>Postgres</ProductName> Operators</TITLE>
<TITLEABBREV>Operators</TITLEABBREV>
<TGROUP COLS="3">
<THEAD>
<ROW>
<ENTRY>Operator</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Usage</ENTRY>
</ROW>
</THEAD>
<TBODY>
<ROW>
<ENTRY> &lt; </ENTRY>
<ENTRY>Less than?</ENTRY>
<ENTRY>1 &lt; 2</ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;= </ENTRY>
<ENTRY>Less than or equal to?</ENTRY>
<ENTRY>1 &lt;= 2</ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;&gt; </ENTRY>
<ENTRY>Not equal?</ENTRY>
<ENTRY>1 &lt;&gt; 2</ENTRY>
</ROW>
<ROW>
<ENTRY> = </ENTRY>
<ENTRY>Equal?</ENTRY>
<ENTRY>1 = 1</ENTRY>
</ROW>
<ROW>
<ENTRY> &gt; </ENTRY>
<ENTRY>Greater than?</ENTRY>
<ENTRY>2 &gt; 1</ENTRY>
</ROW>
<ROW>
<ENTRY> &gt;= </ENTRY>
<ENTRY>Greater than or equal to?</ENTRY>
<ENTRY>2 &gt;= 1</ENTRY>
</ROW>
<ROW>
<ENTRY> || </ENTRY>
<ENTRY>Concatenate strings</ENTRY>
<ENTRY>'Postgre' || 'SQL'</ENTRY>
</ROW>
<ROW>
<ENTRY> !!= </ENTRY>
<ENTRY>NOT IN</ENTRY>
<ENTRY>3 !!= i</ENTRY>
</ROW>
<ROW>
<ENTRY> ~~ </ENTRY>
<ENTRY>LIKE</ENTRY>
<ENTRY>'scrappy,marc,hermit' ~~ '%scrappy%'</ENTRY>
</ROW>
<ROW>
<ENTRY> !~~ </ENTRY>
<ENTRY>NOT LIKE</ENTRY>
<ENTRY>'bruce' !~~ '%al%'</ENTRY>
</ROW>
<ROW>
<ENTRY> ~ </ENTRY>
<ENTRY>Match (regex), case sensitive</ENTRY>
<ENTRY>'thomas' ~ '*.thomas*.'</ENTRY>
</ROW>
<ROW>
<ENTRY> ~* </ENTRY>
<ENTRY>Match (regex), case insensitive</ENTRY>
<ENTRY>'thomas' ~* '*.Thomas*.'</ENTRY>
</ROW>
<ROW>
<ENTRY> !~ </ENTRY>
<ENTRY>Does not match (regex), case sensitive</ENTRY>
<ENTRY>'thomas' !~ '*.Thomas*.'</ENTRY>
</ROW>
<ROW>
<ENTRY> !~* </ENTRY>
<ENTRY>Does not match (regex), case insensitive</ENTRY>
<ENTRY>'thomas' !~ '*.vadim*.'</ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<Para>
<TABLE TOCENTRY="1">
<TITLE><ProductName>Postgres</ProductName> Numerical Operators</TITLE>
<TITLEABBREV>Operators</TITLEABBREV>
<TGROUP COLS="3">
<THEAD>
<ROW>
<ENTRY>Operator</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Usage</ENTRY>
</ROW>
</THEAD>
<TBODY>
<ROW>
<ENTRY> ! </ENTRY>
<ENTRY>Factorial</ENTRY>
<ENTRY>3 !</ENTRY>
</ROW>
<ROW>
<ENTRY> !! </ENTRY>
<ENTRY>Factorial (left operator)</ENTRY>
<ENTRY>!! 3</ENTRY>
</ROW>
<ROW>
<ENTRY> % </ENTRY>
<ENTRY>Modulo</ENTRY>
<ENTRY>5 % 4</ENTRY>
</ROW>
<ROW>
<ENTRY> % </ENTRY>
<ENTRY>Truncate</ENTRY>
<ENTRY>% 4.5</ENTRY>
</ROW>
<ROW>
<ENTRY> * </ENTRY>
<ENTRY>Multiplication</ENTRY>
<ENTRY>2 * 3</ENTRY>
</ROW>
<ROW>
<ENTRY> + </ENTRY>
<ENTRY>Addition</ENTRY>
<ENTRY>2 + 3</ENTRY>
</ROW>
<ROW>
<ENTRY> - </ENTRY>
<ENTRY>Subtraction</ENTRY>
<ENTRY>2 - 3</ENTRY>
</ROW>
<ROW>
<ENTRY> / </ENTRY>
<ENTRY>Division</ENTRY>
<ENTRY>4 / 2</ENTRY>
</ROW>
<ROW>
<ENTRY> : </ENTRY>
<ENTRY>Natural Exponentiation</ENTRY>
<ENTRY>: 3.0</ENTRY>
</ROW>
<ROW>
<ENTRY> ; </ENTRY>
<ENTRY>Natural Logarithm</ENTRY>
<ENTRY>(; 5.0)</ENTRY>
</ROW>
<ROW>
<ENTRY> @ </ENTRY>
<ENTRY>Absolute value</ENTRY>
<ENTRY>@ -5.0</ENTRY>
</ROW>
<ROW>
<ENTRY> ^ </ENTRY>
<ENTRY>Exponentiation</ENTRY>
<ENTRY>2.0 ^ 3.0</ENTRY>
</ROW>
<ROW>
<ENTRY> |/ </ENTRY>
<ENTRY>Square root</ENTRY>
<ENTRY>|/ 25.0</ENTRY>
</ROW>
<ROW>
<ENTRY> ||/ </ENTRY>
<ENTRY>Cube root</ENTRY>
<ENTRY>||/ 27.0</ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<Para>
<TABLE TOCENTRY="1">
<TITLE><ProductName>Postgres</ProductName> Geometric Operators</TITLE>
<TITLEABBREV>Operators</TITLEABBREV>
<TGROUP COLS="3">
<THEAD>
<ROW>
<ENTRY>Operator</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Usage</ENTRY>
</ROW>
</THEAD>
<TBODY>
<ROW>
<ENTRY> + </ENTRY>
<ENTRY>Translation</ENTRY>
<ENTRY>'((0,0),(1,1))'::box + '(2.0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> - </ENTRY>
<ENTRY>Translation</ENTRY>
<ENTRY>'((0,0),(1,1))'::box - '(2.0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> * </ENTRY>
<ENTRY>Scaling/rotation</ENTRY>
<ENTRY>'((0,0),(1,1))'::box * '(2.0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> / </ENTRY>
<ENTRY>Scaling/rotation</ENTRY>
<ENTRY>'((0,0),(2,2))'::box / '(2.0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> # </ENTRY>
<ENTRY>Intersection</ENTRY>
<ENTRY>'((1,-1),(-1,1))' # '((1,1),(-1,-1))'</ENTRY>
</ROW>
<ROW>
<ENTRY> # </ENTRY>
<ENTRY>Number of points in polygon</ENTRY>
<ENTRY># '((1,0),(0,1),(-1,0))'</ENTRY>
</ROW>
<ROW>
<ENTRY> ## </ENTRY>
<ENTRY>Point of closest proximity</ENTRY>
<ENTRY>'(0,0)'::point ## '((2,0),(0,2))'::lseg</ENTRY>
</ROW>
<ROW>
<ENTRY> &amp;&amp; </ENTRY>
<ENTRY>Overlaps?</ENTRY>
<ENTRY>'((0,0),(1,1))'::box &amp;&amp; '((0,0),(2,2))'::box</ENTRY>
</ROW>
<ROW>
<ENTRY> &amp;&lt; </ENTRY>
<ENTRY>Overlaps to left?</ENTRY>
<ENTRY>'((0,0),(1,1))'::box &amp;&lt; '((0,0),(2,2))'::box</ENTRY>
</ROW>
<ROW>
<ENTRY> &amp;&gt; </ENTRY>
<ENTRY>Overlaps to right?</ENTRY>
<ENTRY>'((0,0),(3,3))'::box &amp;&gt; '((0,0),(2,2))'::box</ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;-&gt; </ENTRY>
<ENTRY>Distance between</ENTRY>
<ENTRY>'((0,0),1)'::circle &lt;-&gt; '((5,0),1)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;&lt; </ENTRY>
<ENTRY>Left of?</ENTRY>
<ENTRY>'((0,0),1)'::circle &lt;&lt; '((5,0),1)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;^ </ENTRY>
<ENTRY>Is below?</ENTRY>
<ENTRY>'((0,0),1)'::circle &lt;^ '((0,5),1)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> &gt;&gt; </ENTRY>
<ENTRY>Is right of?</ENTRY>
<ENTRY>'((5,0),1)'::circle &gt;&gt; '((0,0),1)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> &gt;^ </ENTRY>
<ENTRY>Is above?</ENTRY>
<ENTRY>'((0,5),1)'::circle >^ '((0,0),1)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> ?# </ENTRY>
<ENTRY>Intersects or overlaps</ENTRY>
<ENTRY>'((-1,0),(1,0))'::lseg ?# '((-2,-2),(2,2))'::box;</ENTRY>
</ROW>
<ROW>
<ENTRY> ?- </ENTRY>
<ENTRY>Is horizontal?</ENTRY>
<ENTRY>'(1,0)'::point ?- '(0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> ?-| </ENTRY>
<ENTRY>Is perpendicular?</ENTRY>
<ENTRY>'((0,0),(0,1))'::lseg ?-| '((0,0),(1,0))'::lseg</ENTRY>
</ROW>
<ROW>
<ENTRY> @-@ </ENTRY>
<ENTRY>Length or circumference</ENTRY>
<ENTRY>@-@ '((0,0),(1,0))'::path</ENTRY>
</ROW>
<ROW>
<ENTRY> ?| </ENTRY>
<ENTRY>Is vertical?</ENTRY>
<ENTRY>'(0,1)'::point ?| '(0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> ?|| </ENTRY>
<ENTRY>Is parallel?</ENTRY>
<ENTRY>'((-1,0),(1,0))'::lseg ?|| '((-1,2),(1,2))'::lseg</ENTRY>
</ROW>
<ROW>
<ENTRY> @ </ENTRY>
<ENTRY>Contained or on</ENTRY>
<ENTRY>'(1,1)'::point @ '((0,0),2)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> @@ </ENTRY>
<ENTRY>Center of</ENTRY>
<ENTRY>@@ '((0,0),10)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> ~= </ENTRY>
<ENTRY>Same as</ENTRY>
<ENTRY>'((0,0),(1,1))'::polygon ~= '((1,1),(0,0))'::polygon</ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<Para>
The time interval data type <Type>tinterval</Type> is a legacy from the original
date/time types and is not as well supported as the more modern types. There
are several operators for this type.
<TABLE TOCENTRY="1">
<TITLE><ProductName>Postgres</ProductName> Time Interval Operators</TITLE>
<TITLEABBREV>Operators</TITLEABBREV>
<TGROUP COLS="3">
<THEAD>
<ROW>
<ENTRY>Operator</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Usage</ENTRY>
</ROW>
</THEAD>
<TBODY>
<ROW>
<ENTRY> #&lt; </ENTRY>
<ENTRY>Interval less than?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> #&lt;= </ENTRY>
<ENTRY>Interval less than or equal to?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> #&lt;&gt; </ENTRY>
<ENTRY>Interval not equal?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> #= </ENTRY>
<ENTRY>Interval equal?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> #&gt; </ENTRY>
<ENTRY>Interval greater than?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> #&gt;= </ENTRY>
<ENTRY>Interval greater than or equal to?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;#&gt; </ENTRY>
<ENTRY>Convert to time interval</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;&lt; </ENTRY>
<ENTRY>Interval less than?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> | </ENTRY>
<ENTRY>Start of interval</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> ~= </ENTRY>
<ENTRY>Same as</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;?&gt; </ENTRY>
<ENTRY>Time inside interval?</ENTRY>
<ENTRY></ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<Para>
Users may invoke operators using the operator name, as in:
<ProgramListing>
select * from emp where salary < 40000;
</ProgramListing>
Alternatively, users may call the functions that implement the
operators directly. In this case, the query above would be expressed
as:
<ProgramListing>
select * from emp where int4lt(salary, 40000);
</ProgramListing>
<Para>
<Application>psql</Application>
has a <Command>\dd</Command> command to show these operators.
</Chapter>
<Chapter>
<Title>Functions</Title>
<Para>
Many data types have functions available for conversion to other related types.
In addition, there are some type-specific functions. Functions which are also
available through operators are documented as operators only.
</Para>
<Para>
Some functions defined for text are also available for char() and varchar().
</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>
<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> 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> int </ENTRY>
<ENTRY> integer(float) </ENTRY>
<ENTRY> convert floating point to integer </ENTRY>
<ENTRY> integer(2.0) </ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<Para>
Many of the string functions are available for text, varchar(), and char() types.
At the moment, some functions are available only for the text type.
<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> lower(text) </ENTRY>
<ENTRY> text </ENTRY>
<ENTRY> convert text to lower case </ENTRY>
<ENTRY> lower('TOM') </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> position(text,text) </ENTRY>
<ENTRY> text </ENTRY>
<ENTRY> extract 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> upper(text) </ENTRY>
<ENTRY> text </ENTRY>
<ENTRY> convert text to upper case </ENTRY>
<ENTRY> upper('tom') </ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</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> isfinite(abstime) </ENTRY>
<ENTRY> bool </ENTRY>
<ENTRY> TRUE if this is a finite time </ENTRY>
<ENTRY> isfinite('now'::abstime) </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> age(datetime,datetime) </ENTRY>
<ENTRY> timespan </ENTRY>
<ENTRY> span preserving months and years </ENTRY>
<ENTRY> age('now','1957-06-13'::datetime) </ENTRY>
</ROW>
<ROW>
<ENTRY> date_part(text,datetime) </ENTRY>
<ENTRY> float8 </ENTRY>
<ENTRY> specified portion of date field </ENTRY>
<ENTRY> date_part('dow','now'::datetime) </ENTRY>
</ROW>
<ROW>
<ENTRY> date_trunc(text,datetime) </ENTRY>
<ENTRY> datetime </ENTRY>
<ENTRY> truncate date at specified units </ENTRY>
<ENTRY> date_trunc('month','now'::abstime) </ENTRY>
</ROW>
<ROW>
<ENTRY> isfinite(datetime) </ENTRY>
<ENTRY> bool </ENTRY>
<ENTRY> TRUE if this is a finite time </ENTRY>
<ENTRY> isfinite('now'::datetime) </ENTRY>
</ROW>
<ROW>
<ENTRY> abstime(datetime) </ENTRY>
<ENTRY> abstime </ENTRY>
<ENTRY> convert to abstime </ENTRY>
<ENTRY> abstime('now'::datetime) </ENTRY>
</ROW>
<ROW>
<ENTRY> timespan(reltime) </ENTRY>
<ENTRY> timespan </ENTRY>
<ENTRY> convert to timespan </ENTRY>
<ENTRY> timespan('4 hours'::reltime) </ENTRY>
</ROW>
<ROW>
<ENTRY> datetime(date,time) </ENTRY>
<ENTRY> datetime </ENTRY>
<ENTRY> convert to datetime </ENTRY>
<ENTRY> datetime('1998-02-25'::date,'06:41'::time) </ENTRY>
</ROW>
<ROW>
<ENTRY> date_part(text,timespan) </ENTRY>
<ENTRY> float8 </ENTRY>
<ENTRY> specified portion of time field </ENTRY>
<ENTRY> date_part('hour','4 hrs 3 mins'::timespan) </ENTRY>
</ROW>
<ROW>
<ENTRY> isfinite(timespan) </ENTRY>
<ENTRY> bool </ENTRY>
<ENTRY> TRUE if this is 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>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<Para>
<TABLE TOCENTRY="1">
<TITLE>Geometric Functions</TITLE>
<TGROUP COLS="3">
<THEAD>
<ROW>
<ENTRY>Function</ENTRY>
<ENTRY>Returns</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Example</ENTRY>
</ROW>
</THEAD>
<TBODY>
<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> area(box) </ENTRY>
<ENTRY> float8 </ENTRY>
<ENTRY> area of box </ENTRY>
<ENTRY> area('((0,0),(1,1))'::box) </ENTRY>
</ROW>
<ROW>
<ENTRY> isopen(path) </ENTRY>
<ENTRY> bool </ENTRY>
<ENTRY> TRUE if this is an open path </ENTRY>
<ENTRY> isopen('[(0,0),(1,1),(2,0)]'::path) </ENTRY>
</ROW>
<ROW>
<ENTRY> isclosed(path) </ENTRY>
<ENTRY> bool </ENTRY>
<ENTRY> TRUE if this is a closed path </ENTRY>
<ENTRY> isclosed('((0,0),(1,1),(2,0))'::path) </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> polygon(npts,circle) </ENTRY>
<ENTRY> polygon </ENTRY>
<ENTRY> convert to polygon with npts points </ENTRY>
<ENTRY> polygon(12,'((0,0),2.0)'::circle) </ENTRY>
</ROW>
<ROW>
<ENTRY> center(circle) </ENTRY>
<ENTRY> float8 </ENTRY>
<ENTRY> center of object </ENTRY>
<ENTRY> center('((0,0),2.0)'::circle) </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> diameter(circle) </ENTRY>
<ENTRY> float8 </ENTRY>
<ENTRY> diameter of circle </ENTRY>
<ENTRY> diameter('((0,0),2.0)'::circle) </ENTRY>
</ROW>
<ROW>
<ENTRY> area(circle) </ENTRY>
<ENTRY> float8 </ENTRY>
<ENTRY> area of circle </ENTRY>
<ENTRY> area('((0,0),2.0)'::circle) </ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<Para>
SQL92 defines functions with specific syntax. Some of these
are implemented using other <ProductName>Postgres</ProductName> functions.
</Para>
<Para>
<TABLE TOCENTRY="1">
<TITLE><Acronym>SQL92</Acronym> Text Functions</TITLE>
<TGROUP COLS="3">
<THEAD>
<ROW>
<ENTRY>Function</ENTRY>
<ENTRY>Returns</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Example</ENTRY>
</ROW>
</THEAD>
<TBODY>
<ROW>
<ENTRY> position(text in text) </ENTRY>
<ENTRY> int4 </ENTRY>
<ENTRY> extract specified substring </ENTRY>
<ENTRY> position('o' in 'Tom') </ENTRY>
</ROW>
<ROW>
<ENTRY> substring(text [from int] [for int]) </ENTRY>
<ENTRY> text </ENTRY>
<ENTRY> extract specified substring </ENTRY>
<ENTRY> substring('Tom' from 2 for 2) </ENTRY>
</ROW>
<ROW>
<ENTRY> trim([leading|trailing|both] [text] from text) </ENTRY>
<ENTRY> text </ENTRY>
<ENTRY> trim characters from text </ENTRY>
<ENTRY> trim(both 'x' from 'xTomx') </ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>

2
doc/src/sgml/docguide.sgml
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@ -239,7 +239,7 @@ right, and I can verify the document with "nsgmls -s docguide.sgml".
<title>Building Documentation</title>
<para>
GNU <programname>make</programname> is used to build documentation from the DocBook sources.
GNU <application>make</application> is used to build documentation from the DocBook sources.
There are a few environment definitions which may need to be set or modified for your installation.
The <filename>Makefile</filename> looks for
<filename>doc/../src/Makefile</filename>

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<Chapter>
<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>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>
<title>String Functions</title>
<Para>
SQL92 defines string functions with specific syntax. Some of these
are implemented using other <ProductName>Postgres</ProductName> functions.
</Para>
<Para>
<TABLE TOCENTRY="1">
<TITLE><Acronym>SQL92</Acronym> Text Functions</TITLE>
<TGROUP COLS="4">
<THEAD>
<ROW>
<ENTRY>Function</ENTRY>
<ENTRY>Returns</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Example</ENTRY>
</ROW>
</THEAD>
<TBODY>
<ROW>
<ENTRY> position(text in text) </ENTRY>
<ENTRY> int4 </ENTRY>
<ENTRY> location of specified substring </ENTRY>
<ENTRY> position('o' in 'Tom') </ENTRY>
</ROW>
<ROW>
<ENTRY> substring(text [from int] [for int]) </ENTRY>
<ENTRY> text </ENTRY>
<ENTRY> extract specified substring </ENTRY>
<ENTRY> substring('Tom' from 2 for 2) </ENTRY>
</ROW>
<ROW>
<ENTRY> trim([leading|trailing|both] [text] from text) </ENTRY>
<ENTRY> text </ENTRY>
<ENTRY> trim characters from text </ENTRY>
<ENTRY> trim(both 'x' from 'xTomx') </ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<Para>
Many 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> lower(text) </ENTRY>
<ENTRY> text </ENTRY>
<ENTRY> convert text to lower case </ENTRY>
<ENTRY> lower('TOM') </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> position(text,text) </ENTRY>
<ENTRY> text </ENTRY>
<ENTRY> extract 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> 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>
<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>
Most functions explicitly defined for text will work for char() and varchar() arguments.
</para>
<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> span preserving 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> specified portion of date field </ENTRY>
<ENTRY> date_part('dow','now'::datetime) </ENTRY>
</ROW>
<ROW>
<ENTRY> date_part(text,timespan) </ENTRY>
<ENTRY> float8 </ENTRY>
<ENTRY> specified portion of time field </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 at specified units </ENTRY>
<ENTRY> date_trunc('month','now'::abstime) </ENTRY>
</ROW>
<ROW>
<ENTRY> isfinite(abstime) </ENTRY>
<ENTRY> bool </ENTRY>
<ENTRY> TRUE if this is a finite time </ENTRY>
<ENTRY> isfinite('now'::abstime) </ENTRY>
</ROW>
<ROW>
<ENTRY> isfinite(datetime) </ENTRY>
<ENTRY> bool </ENTRY>
<ENTRY> TRUE if this is a finite time </ENTRY>
<ENTRY> isfinite('now'::datetime) </ENTRY>
</ROW>
<ROW>
<ENTRY> isfinite(timespan) </ENTRY>
<ENTRY> bool </ENTRY>
<ENTRY> TRUE if this is 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>
<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> TRUE if this is a closed path </ENTRY>
<ENTRY> isclosed('((0,0),(1,1),(2,0))'::path) </ENTRY>
</ROW>
<ROW>
<ENTRY> isopen(path) </ENTRY>
<ENTRY> bool </ENTRY>
<ENTRY> TRUE if this is 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 variant </ENTRY>
<ENTRY> popen('[(0,0),(1,1),(2,0)]'::path) </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> points(path) </ENTRY>
<ENTRY> int4 </ENTRY>
<ENTRY> number of points in path </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 variant </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 of box </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 polygon with 12 points </ENTRY>
<ENTRY> polygon('((0,0),2.0)'::circle) </ENTRY>
</ROW>
<ROW>
<ENTRY> polygon(npts,circle) </ENTRY>
<ENTRY> polygon </ENTRY>
<ENTRY> convert to polygon with npts points </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>
</chapter>

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<Chapter>
<Title>Operators</Title>
<Abstract>
<Para>
Describes the built-in operators available in <ProductName>Postgres</ProductName>.
</Para>
</Abstract>
<Para>
<ProductName>Postgres</ProductName> provides a large number of built-in operators on system types.
These operators are declared in the system catalog
pg_operator. Every entry in pg_operator includes
the name of the procedure that implements the operator and the
class <Acronym>OIDs</Acronym> of the input and output types.
<Para>
To view all variations of the <Quote>||</Quote> string concatenation operator, try
<ProgramListing>
SELECT oprleft, oprright, oprresult, oprcode
FROM pg_operator WHERE oprname = '||';
oprleft|oprright|oprresult|oprcode
-------+--------+---------+-------
25| 25| 25|textcat
1042| 1042| 1042|textcat
1043| 1043| 1043|textcat
(3 rows)
</ProgramListing>
</Para>
<sect1>
<title>General Operators</title>
<para>
The operators listed here are defined for a number of native data types, ranging
from numeric types to data/time types.
<Para>
<TABLE TOCENTRY="1">
<TITLE><ProductName>Postgres</ProductName> Operators</TITLE>
<TITLEABBREV>Operators</TITLEABBREV>
<TGROUP COLS="3">
<THEAD>
<ROW>
<ENTRY>Operator</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Usage</ENTRY>
</ROW>
</THEAD>
<TBODY>
<ROW>
<ENTRY> &lt; </ENTRY>
<ENTRY>Less than?</ENTRY>
<ENTRY>1 &lt; 2</ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;= </ENTRY>
<ENTRY>Less than or equal to?</ENTRY>
<ENTRY>1 &lt;= 2</ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;&gt; </ENTRY>
<ENTRY>Not equal?</ENTRY>
<ENTRY>1 &lt;&gt; 2</ENTRY>
</ROW>
<ROW>
<ENTRY> = </ENTRY>
<ENTRY>Equal?</ENTRY>
<ENTRY>1 = 1</ENTRY>
</ROW>
<ROW>
<ENTRY> &gt; </ENTRY>
<ENTRY>Greater than?</ENTRY>
<ENTRY>2 &gt; 1</ENTRY>
</ROW>
<ROW>
<ENTRY> &gt;= </ENTRY>
<ENTRY>Greater than or equal to?</ENTRY>
<ENTRY>2 &gt;= 1</ENTRY>
</ROW>
<ROW>
<ENTRY> || </ENTRY>
<ENTRY>Concatenate strings</ENTRY>
<ENTRY>'Postgre' || 'SQL'</ENTRY>
</ROW>
<ROW>
<ENTRY> !!= </ENTRY>
<ENTRY>NOT IN</ENTRY>
<ENTRY>3 !!= i</ENTRY>
</ROW>
<ROW>
<ENTRY> ~~ </ENTRY>
<ENTRY>LIKE</ENTRY>
<ENTRY>'scrappy,marc,hermit' ~~ '%scrappy%'</ENTRY>
</ROW>
<ROW>
<ENTRY> !~~ </ENTRY>
<ENTRY>NOT LIKE</ENTRY>
<ENTRY>'bruce' !~~ '%al%'</ENTRY>
</ROW>
<ROW>
<ENTRY> ~ </ENTRY>
<ENTRY>Match (regex), case sensitive</ENTRY>
<ENTRY>'thomas' ~ '*.thomas*.'</ENTRY>
</ROW>
<ROW>
<ENTRY> ~* </ENTRY>
<ENTRY>Match (regex), case insensitive</ENTRY>
<ENTRY>'thomas' ~* '*.Thomas*.'</ENTRY>
</ROW>
<ROW>
<ENTRY> !~ </ENTRY>
<ENTRY>Does not match (regex), case sensitive</ENTRY>
<ENTRY>'thomas' !~ '*.Thomas*.'</ENTRY>
</ROW>
<ROW>
<ENTRY> !~* </ENTRY>
<ENTRY>Does not match (regex), case insensitive</ENTRY>
<ENTRY>'thomas' !~ '*.vadim*.'</ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<sect1>
<title>Numerical Operators</title>
<Para>
<TABLE TOCENTRY="1">
<TITLE><ProductName>Postgres</ProductName> Numerical Operators</TITLE>
<TITLEABBREV>Operators</TITLEABBREV>
<TGROUP COLS="3">
<THEAD>
<ROW>
<ENTRY>Operator</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Usage</ENTRY>
</ROW>
</THEAD>
<TBODY>
<ROW>
<ENTRY> ! </ENTRY>
<ENTRY>Factorial</ENTRY>
<ENTRY>3 !</ENTRY>
</ROW>
<ROW>
<ENTRY> !! </ENTRY>
<ENTRY>Factorial (left operator)</ENTRY>
<ENTRY>!! 3</ENTRY>
</ROW>
<ROW>
<ENTRY> % </ENTRY>
<ENTRY>Modulo</ENTRY>
<ENTRY>5 % 4</ENTRY>
</ROW>
<ROW>
<ENTRY> % </ENTRY>
<ENTRY>Truncate</ENTRY>
<ENTRY>% 4.5</ENTRY>
</ROW>
<ROW>
<ENTRY> * </ENTRY>
<ENTRY>Multiplication</ENTRY>
<ENTRY>2 * 3</ENTRY>
</ROW>
<ROW>
<ENTRY> + </ENTRY>
<ENTRY>Addition</ENTRY>
<ENTRY>2 + 3</ENTRY>
</ROW>
<ROW>
<ENTRY> - </ENTRY>
<ENTRY>Subtraction</ENTRY>
<ENTRY>2 - 3</ENTRY>
</ROW>
<ROW>
<ENTRY> / </ENTRY>
<ENTRY>Division</ENTRY>
<ENTRY>4 / 2</ENTRY>
</ROW>
<ROW>
<ENTRY> : </ENTRY>
<ENTRY>Natural Exponentiation</ENTRY>
<ENTRY>: 3.0</ENTRY>
</ROW>
<ROW>
<ENTRY> ; </ENTRY>
<ENTRY>Natural Logarithm</ENTRY>
<ENTRY>(; 5.0)</ENTRY>
</ROW>
<ROW>
<ENTRY> @ </ENTRY>
<ENTRY>Absolute value</ENTRY>
<ENTRY>@ -5.0</ENTRY>
</ROW>
<ROW>
<ENTRY> ^ </ENTRY>
<ENTRY>Exponentiation</ENTRY>
<ENTRY>2.0 ^ 3.0</ENTRY>
</ROW>
<ROW>
<ENTRY> |/ </ENTRY>
<ENTRY>Square root</ENTRY>
<ENTRY>|/ 25.0</ENTRY>
</ROW>
<ROW>
<ENTRY> ||/ </ENTRY>
<ENTRY>Cube root</ENTRY>
<ENTRY>||/ 27.0</ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<sect1>
<title>Geometric Operators</title>
<Para>
<TABLE TOCENTRY="1">
<TITLE><ProductName>Postgres</ProductName> Geometric Operators</TITLE>
<TITLEABBREV>Operators</TITLEABBREV>
<TGROUP COLS="3">
<THEAD>
<ROW>
<ENTRY>Operator</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Usage</ENTRY>
</ROW>
</THEAD>
<TBODY>
<ROW>
<ENTRY> + </ENTRY>
<ENTRY>Translation</ENTRY>
<ENTRY>'((0,0),(1,1))'::box + '(2.0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> - </ENTRY>
<ENTRY>Translation</ENTRY>
<ENTRY>'((0,0),(1,1))'::box - '(2.0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> * </ENTRY>
<ENTRY>Scaling/rotation</ENTRY>
<ENTRY>'((0,0),(1,1))'::box * '(2.0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> / </ENTRY>
<ENTRY>Scaling/rotation</ENTRY>
<ENTRY>'((0,0),(2,2))'::box / '(2.0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> # </ENTRY>
<ENTRY>Intersection</ENTRY>
<ENTRY>'((1,-1),(-1,1))' # '((1,1),(-1,-1))'</ENTRY>
</ROW>
<ROW>
<ENTRY> # </ENTRY>
<ENTRY>Number of points in polygon</ENTRY>
<ENTRY># '((1,0),(0,1),(-1,0))'</ENTRY>
</ROW>
<ROW>
<ENTRY> ## </ENTRY>
<ENTRY>Point of closest proximity</ENTRY>
<ENTRY>'(0,0)'::point ## '((2,0),(0,2))'::lseg</ENTRY>
</ROW>
<ROW>
<ENTRY> &amp;&amp; </ENTRY>
<ENTRY>Overlaps?</ENTRY>
<ENTRY>'((0,0),(1,1))'::box &amp;&amp; '((0,0),(2,2))'::box</ENTRY>
</ROW>
<ROW>
<ENTRY> &amp;&lt; </ENTRY>
<ENTRY>Overlaps to left?</ENTRY>
<ENTRY>'((0,0),(1,1))'::box &amp;&lt; '((0,0),(2,2))'::box</ENTRY>
</ROW>
<ROW>
<ENTRY> &amp;&gt; </ENTRY>
<ENTRY>Overlaps to right?</ENTRY>
<ENTRY>'((0,0),(3,3))'::box &amp;&gt; '((0,0),(2,2))'::box</ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;-&gt; </ENTRY>
<ENTRY>Distance between</ENTRY>
<ENTRY>'((0,0),1)'::circle &lt;-&gt; '((5,0),1)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;&lt; </ENTRY>
<ENTRY>Left of?</ENTRY>
<ENTRY>'((0,0),1)'::circle &lt;&lt; '((5,0),1)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;^ </ENTRY>
<ENTRY>Is below?</ENTRY>
<ENTRY>'((0,0),1)'::circle &lt;^ '((0,5),1)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> &gt;&gt; </ENTRY>
<ENTRY>Is right of?</ENTRY>
<ENTRY>'((5,0),1)'::circle &gt;&gt; '((0,0),1)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> &gt;^ </ENTRY>
<ENTRY>Is above?</ENTRY>
<ENTRY>'((0,5),1)'::circle >^ '((0,0),1)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> ?# </ENTRY>
<ENTRY>Intersects or overlaps</ENTRY>
<ENTRY>'((-1,0),(1,0))'::lseg ?# '((-2,-2),(2,2))'::box;</ENTRY>
</ROW>
<ROW>
<ENTRY> ?- </ENTRY>
<ENTRY>Is horizontal?</ENTRY>
<ENTRY>'(1,0)'::point ?- '(0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> ?-| </ENTRY>
<ENTRY>Is perpendicular?</ENTRY>
<ENTRY>'((0,0),(0,1))'::lseg ?-| '((0,0),(1,0))'::lseg</ENTRY>
</ROW>
<ROW>
<ENTRY> @-@ </ENTRY>
<ENTRY>Length or circumference</ENTRY>
<ENTRY>@-@ '((0,0),(1,0))'::path</ENTRY>
</ROW>
<ROW>
<ENTRY> ?| </ENTRY>
<ENTRY>Is vertical?</ENTRY>
<ENTRY>'(0,1)'::point ?| '(0,0)'::point</ENTRY>
</ROW>
<ROW>
<ENTRY> ?|| </ENTRY>
<ENTRY>Is parallel?</ENTRY>
<ENTRY>'((-1,0),(1,0))'::lseg ?|| '((-1,2),(1,2))'::lseg</ENTRY>
</ROW>
<ROW>
<ENTRY> @ </ENTRY>
<ENTRY>Contained or on</ENTRY>
<ENTRY>'(1,1)'::point @ '((0,0),2)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> @@ </ENTRY>
<ENTRY>Center of</ENTRY>
<ENTRY>@@ '((0,0),10)'::circle</ENTRY>
</ROW>
<ROW>
<ENTRY> ~= </ENTRY>
<ENTRY>Same as</ENTRY>
<ENTRY>'((0,0),(1,1))'::polygon ~= '((1,1),(0,0))'::polygon</ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<sect1>
<title>Time Interval Operators</title>
<Para>
The time interval data type <Type>tinterval</Type> is a legacy from the original
date/time types and is not as well supported as the more modern types. There
are several operators for this type.
<TABLE TOCENTRY="1">
<TITLE><ProductName>Postgres</ProductName> Time Interval Operators</TITLE>
<TITLEABBREV>Operators</TITLEABBREV>
<TGROUP COLS="3">
<THEAD>
<ROW>
<ENTRY>Operator</ENTRY>
<ENTRY>Description</ENTRY>
<ENTRY>Usage</ENTRY>
</ROW>
</THEAD>
<TBODY>
<ROW>
<ENTRY> #&lt; </ENTRY>
<ENTRY>Interval less than?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> #&lt;= </ENTRY>
<ENTRY>Interval less than or equal to?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> #&lt;&gt; </ENTRY>
<ENTRY>Interval not equal?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> #= </ENTRY>
<ENTRY>Interval equal?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> #&gt; </ENTRY>
<ENTRY>Interval greater than?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> #&gt;= </ENTRY>
<ENTRY>Interval greater than or equal to?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;#&gt; </ENTRY>
<ENTRY>Convert to time interval</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;&lt; </ENTRY>
<ENTRY>Interval less than?</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> | </ENTRY>
<ENTRY>Start of interval</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> ~= </ENTRY>
<ENTRY>Same as</ENTRY>
<ENTRY></ENTRY>
</ROW>
<ROW>
<ENTRY> &lt;?&gt; </ENTRY>
<ENTRY>Time inside interval?</ENTRY>
<ENTRY></ENTRY>
</ROW>
</TBODY>
</TGROUP>
</TABLE>
</Para>
<Para>
Users may invoke operators using the operator name, as in:
<ProgramListing>
select * from emp where salary < 40000;
</ProgramListing>
Alternatively, users may call the functions that implement the
operators directly. In this case, the query above would be expressed
as:
<ProgramListing>
select * from emp where int4lt(salary, 40000);
</ProgramListing>
<Para>
<Application>psql</Application>
has a command (<Command>\dd</Command>) to show these operators.
</Chapter>

6
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View File

@ -18,6 +18,9 @@
<!entity environ SYSTEM "environ.sgml">
<!entity manage SYSTEM "manage.sgml">
<!entity datatype SYSTEM "datatype.sgml">
<!entity oper SYSTEM "oper.sgml">
<!entity func SYSTEM "func.sgml">
<!entity typeconv SYSTEM "typeconv.sgml">
<!entity array SYSTEM "array.sgml">
<!entity inherit SYSTEM "inherit.sgml">
<!entity query-ug SYSTEM "query-ug.sgml">
@ -162,6 +165,9 @@ Information for users.
&environ;
&manage;
&datatype;
&oper;
&func;
&typeconv;
&array;
&inherit;
&query-ug;

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doc/src/sgml/release.sgml
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653
doc/src/sgml/typeconv.sgml Normal file
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@ -0,0 +1,653 @@
<chapter>
<title>Type Conversion</title>
<para>
<acronym>SQL</acronym> queries can, intentionally or not, require
mixing of different data types in the same expression.
<productname>Postgres</productname> has extensive facilities for
evaluating mixed-type expressions.
<para>
In many cases a user will not need
to understand the details of the type conversion mechanism.
However, the implicit conversions done by <productname>Postgres</productname>
can affect the apparent results of a query, and these results
can be tailored by a user or programmer
using <emphasis>explicit</emphasis> type coersion.
<para>
This chapter introduces the <productname>Postgres</productname>
type conversion mechanisms and conventions.
Refer to the relevant sections in the User's Guide and Programmer's Guide
for more information on specific data types and allowed functions and operators.
<para>
The Programmer's Guide has more details on the exact algorithms used for
implicit type conversion and coersion.
<sect1>
<title>Overview</title>
<para>
<acronym>SQL</acronym> is a strongly typed language. That is, every data item
has an associated data type which determines its behavior and allowed usage.
<productname>Postgres</productname> has an extensible type system which is
much more general and flexible than other <acronym>RDBMS</acronym> implementations.
Hence, most type conversion behavior in <productname>Postgres</productname>
should be governed by general rules rather than by ad-hoc heuristics to allow
mixed-type expressions to be meaningful, even with user-defined types.
<para>
The <productname>Postgres</productname> scanner/parser decodes lexical elements
into only five fundamental categories: integers, floats, strings, names, and keywords.
Most extended types are first tokenized into strings. The <acronym>SQL</acronym>
language definition allows specifying type names with strings, and this mechanism
is used by <productname>Postgres</productname>
to start the parser down the correct path. For example, the query
<programlisting>
tgl=> SELECT text 'Origin' AS "Label", point '(0,0)' AS "Value";
Label |Value
------+-----
Origin|(0,0)
(1 row)
</programlisting>
has two strings, of type <type>text</type> and <type>point</type>.
If a type is not specified, then the placeholder type <type>unknown</type>
is assigned initially, to be resolved in later stages as described below.
<para>
There are four fundamental <acronym>SQL</acronym> constructs requiring
distinct type conversion rules in the <productname>Postgres</productname>
parser:
<variablelist>
<varlistentry>
<term>
Operators
</term>
<listitem>
<para>
<productname>Postgres</productname> allows expressions with
left- and right-unary (one argument) operators,
as well as binary (two argument) operators.
</listitem>
</varlistentry>
<varlistentry>
<term>
Function calls
</term>
<listitem>
<para>
Much of the <productname>Postgres</productname> type system is built around a rich set of
functions. Function calls have one or more arguments which, for any specific query,
must be matched to the functions available in the system catalog.
</listitem>
</varlistentry>
<varlistentry>
<term>
Query targets
</term>
<listitem>
<para>
<acronym>SQL</acronym> INSERT statements place the results of query into a table. The expressions
in the query must be matched up with, and perhaps converted to, the target columns of the insert.
</listitem>
</varlistentry>
<varlistentry>
<term>
UNION queries
</term>
<listitem>
<para>
Since all select results from a UNION SELECT statement must appear in a single set of columns, the types
of each SELECT clause must be matched up and converted to a uniform set.
</listitem>
</varlistentry>
</variablelist>
<para>
Many of the general type conversion rules use simple conventions built on
the <productname>Postgres</productname> function and operator system tables.
There are some heuristics included in the conversion rules to better support
conventions for the <acronym>SQL92</acronym> standard native types such as
<type>smallint</type>, <type>integer</type>, and <type>float</type>.
<para>
The <productname>Postgres</productname> parser uses the convention that all
type conversion functions take a single argument of the source type and are
named with the same name as the target type. Any function meeting this
criteria is considered to be a valid conversion function, and may be used
by the parser as such. This simple assumption gives the parser the power
to explore type conversion possibilities without hardcoding, allowing
extended user-defined types to use these same features transparently.
<para>
An additional heuristic is provided in the parser to allow better guesses
at proper behavior for <acronym>SQL</acronym> standard types. There are
five categories of types defined: boolean, string, numeric, geometric,
and user-defined. Each category, with the exception of user-defined, has
a "preferred type" which is used to resolve ambiguities in candidates.
Each "user-defined" type is its own "preferred type", so ambiguous
expressions (those with multiple candidate parsing solutions)
with only one user-defined type can resolve to a single best choice, while those with
multiple user-defined types will remain ambiguous and throw an error.
<para>
Ambiguous expressions which have candidate solutions within only one type category are
likely to resolve, while ambiguous expressions with candidates spanning multiple
categories are likely to throw an error and ask for clarification from the user.
<sect2>
<title>Guidelines</title>
<para>
All type conversion rules are designed with several principles in mind:
<itemizedlist mark="bullet" spacing="compact">
<listitem>
<para>
Implicit conversions should never have suprising or unpredictable outcomes.
<listitem>
<para>
User-defined types, of which the parser has no apriori knowledge, should be
"higher" in the type heirarchy. In mixed-type expressions, native types shall always
be converted to a user-defined type (of course, only if conversion is necessary).
<listitem>
<para>
User-defined types are not related. Currently, <productname>Postgres</productname>
does not have information available to it on relationships between types, other than
hardcoded heuristics for built-in types and implicit relationships based on available functions
in the catalog.
<listitem>
<para>
There should be no extra overhead from the parser or executor
if a query does not need implicit type conversion.
That is, if a query is well formulated and the types already match up, then the query should proceed
without spending extra time in the parser and without introducing unnecessary implicit conversion
functions into the query.
<para>
Additionally, if a query usually requires an implicit conversion for a function, and
if then the user defines an explicit function with the correct argument types, the parser
should use this new function and will no longer do the implicit conversion using the old function.
</itemizedlist>
<sect1>
<title>Operators</title>
<sect2>
<title>Conversion Procedure</title>
<para>
<procedure>
<title>Operator Evaluation</title>
<para>
<step performance="required">
<para>
Check for an exact match in the pg_operator system catalog.
<substeps>
<step performance="optional">
<para>
If one argument of a binary operator is <type>unknown</type>,
then assume it is the same type as the other argument.
<step performance="required">
<para>
Reverse the arguments, and look for an exact match with an operator which
points to itself as being commutative.
If found, then reverse the arguments in the parse tree and use this operator.
</substeps>
<step performance="required">
<para>
Look for the best match.
<substeps>
<step performance="optional">
<para>
Make a list of all operators of the same name.
<step performance="required">
<para>
If only one operator is in the list, use it if the input type can be coerced,
and throw an error if the type cannot be coerced.
<step performance="required">
<para>
Keep all operators with the most explicit matches for types. Keep all if there
are no explicit matches and move to the next step.
If only one candidate remains, use it if the type can be coerced.
<step performance="required">
<para>
If any input arguments are "unknown", categorize the input candidates as
boolean, numeric, string, geometric, or user-defined. If there is a mix of
categories, or more than one user-defined type, throw an error because
the correct choice cannot be deduced without more clues.
If only one category is present, then assign the "preferred type"
to the input column which had been previously "unknown".
<step performance="required">
<para>
Choose the candidate with the most exact type matches, and which matches
the "preferred type" for each column category from the previous step.
If there is still more than one candidate, or if there are none,
then throw an error.
</substeps>
</procedure>
<sect2>
<title>Examples</title>
<sect3>
<title>Exponentiation Operator</title>
<para>
There is only one exponentiation
operator defined in the catalog, and it takes <type>float8</type> arguments.
The scanner assigns an initial type of <type>int4</type> to both arguments
of this query expression:
<programlisting>
tgl=> select 2 ^ 3 AS "Exp";
Exp
---
8
(1 row)
</programlisting>
So the parser does a type conversion on both operands and the query
is equivalent to
<programlisting>
tgl=> select float8(2) ^ float8(3) AS "Exp";
Exp
---
8
(1 row)
</programlisting>
or
<programlisting>
tgl=> select 2.0 ^ 3.0 AS "Exp";
Exp
---
8
(1 row)
</programlisting>
<note>
<para>
This last form has the least overhead, since no functions are called to do
implicit type conversion. This is not an issue for small queries, but may
have an impact on the performance of queries involving large tables.
</note>
<sect3>
<title>String Concatenation</title>
<para>
A string-like syntax is used for working with string types as well as for
working with complex extended types.
Strings with unspecified type are matched with likely operator candidates.
<para>
One unspecified argument:
<programlisting>
tgl=> SELECT text 'abc' || 'def' AS "Text and Unknown";
Text and Unknown
----------------
abcdef
(1 row)
</programlisting>
<para>
In this case the parser looks to see if there is an operator taking <type>text</type>
for both arguments. Since there is, it assumes that the second argument should
be interpreted as of type <type>text</type>.
<para>
Concatenation on unspecified types:
<programlisting>
tgl=> SELECT 'abc' || 'def' AS "Unspecified";
Unspecified
-----------
abcdef
(1 row)
</programlisting>
<para>
In this case there is no initial hint for which type to use, since no types
are specified in the query. So, the parser looks for all candidate operators
and finds that all arguments for all the candidates are string types. It chooses
the "preferred type" for strings, <type>text</type>, for this query.
<note>
<para>
If a user defines a new type and defines an operator <quote>||</quote> to work
with it, then this query would no longer succeed as written. The parser would
now have candidate types from two categories, and could not decide which to use.
</note>
<sect3>
<title>Factorial</title>
<para>
This example illustrates an interesting result. Traditionally, the
factorial operator is defined for integers only. The <productname>Postgres</productname>
operator catalog has only one entry for factorial, taking an integer operand.
If given a non-integer numeric argument, <productname>Postgres</productname>
will try to convert that argument to an integer for evaluation of the
factorial.
<programlisting>
tgl=> select (4.3 !);
?column?
--------
24
(1 row)
</programlisting>
<note>
<para>
Of course, this leads to a mathematically suspect result,
since in principle the factorial of a non-integer is not defined.
However, the role of a database is not to teach mathematics, but
to be a tool for data manipulation. If a user chooses to take the
factorial of a floating point number, <productname>Postgres</productname>
will try to oblige.
</note>
<sect1>
<title>Functions</title>
<para>
<procedure>
<title>Function Evaluation</title>
<step performance="required">
<para>
Check for an exact match in the pg_proc system catalog.
<step performance="required">
<para>
Look for the best match.
<substeps>
<step performance="required">
<para>
Make a list of all functions of the same name with the same number of arguments.
<step performance="required">
<para>
If only one function is in the list, use it if the input types can be coerced,
and throw an error if the types cannot be coerced.
<step performance="required">
<para>
Keep all functions with the most explicit matches for types. Keep all if there
are no explicit matches and move to the next step.
If only one candidate remains, use it if the type can be coerced.
<step performance="required">
<para>
If any input arguments are "unknown", categorize the input candidate arguments as
boolean, numeric, string, geometric, or user-defined. If there is a mix of
categories, or more than one user-defined type, throw an error because
the correct choice cannot be deduced without more clues.
If only one category is present, then assign the "preferred type"
to the input column which had been previously "unknown".
<step performance="required">
<para>
Choose the candidate with the most exact type matches, and which matches
the "preferred type" for each column category from the previous step.
If there is still more than one candidate, or if there are none,
then throw an error.
</substeps>
</procedure>
<sect2>
<title>Examples</title>
<sect3>
<title>Factorial Function</title>
<para>
There is only one factorial function defined in the pg_proc catalog.
So the following query automatically converts the <type>int2</type> argument
to <type>int4</type>:
<programlisting>
tgl=> select int4fac(int2 '4');
int4fac
-------
24
(1 row)
</programlisting>
and is actually transformed by the parser to
<programlisting>
tgl=> select int4fac(int4(int2 '4'));
int4fac
-------
24
(1 row)
</programlisting>
<sect3>
<title>Substring Function</title>
<para>
There are two <function>substr</function> functions declared in pg_proc. However,
only one takes two arguments, of types <type>text</type> and <type>int4</type>.
<para>
If called with a string constant of unspecified type, the type is matched up
directly with the only candidate function type:
<programlisting>
tgl=> select substr('1234', 3);
substr
------
34
(1 row)
</programlisting>
<para>
If the string is declared to be of type <type>varchar</type>, as might be the case
if it comes from a table, then the parser will try to coerce it to become <type>text</type>:
<programlisting>
tgl=> select substr(varchar '1234', 3);
substr
------
34
(1 row)
</programlisting>
which is transformed by the parser to become
<programlisting>
tgl=> select substr(text(varchar '1234'), 3);
substr
------
34
(1 row)
</programlisting>
<note>
<para>
There are some heuristics in the parser to optimize the relationship between the
<type>char</type>, <type>varchar</type>, and <type>text</type> types.
For this case, <function>substr</function> is called directly with the <type>varchar</type> string
rather than inserting an explicit conversion call.
</note>
<para>
And, if the function is called with an <type>int4</type>, the parser will
try to convert that to <type>text</type>:
<programlisting>
tgl=> select substr(1234, 3);
substr
------
34
(1 row)
</programlisting>
actually executes as
<programlisting>
tgl=> select substr(text(1234), 3);
substr
------
34
(1 row)
</programlisting>
<sect1>
<title>Query Targets</title>
<para>
<procedure>
<title>Target Evaluation</title>
<step performance="required">
<para>
Check for an exact match with the target.
<step performance="required">
<para>
Try to coerce the expression directly to the target type if necessary.
<step performance="required">
<para>
If the target is a fixed-length type (e.g. <type>char</type> or <type>varchar</type>
declared with a length) then try to find a sizing function of the same name
as the type taking two arguments, the first the type name and the second an
integer length.
</procedure>
<sect2>
<title>Examples</title>
<sect3>
<title><type>varchar</type> Storage</title>
<para>
For a target column declared as <type>varchar(4)</type> the following query
ensures that the target is sized correctly:
<programlisting>
tgl=> CREATE TABLE vv (v varchar(4));
CREATE
tgl=> INSERT INTO vv SELECT 'abc' || 'def';
INSERT 392905 1
tgl=> select * from vv;
v
----
abcd
(1 row)
</programlisting>
<sect1>
<title>UNION Queries</title>
<para>
The UNION construct is somewhat different in that it must match up
possibly dissimilar types to become a single result set.
<procedure>
<title>UNION Evaluation</title>
<step performance="required">
<para>
Check for identical types for all results.
<step performance="required">
<para>
Coerce each result from the UNION clauses to match the type of the
first SELECT clause or the target column.
</procedure>
<sect2>
<title>Examples</title>
<sect3>
<title>Underspecified Types</title>
<para>
<programlisting>
tgl=> SELECT text 'a' AS "Text" UNION SELECT 'b';
Text
----
a
b
(2 rows)
</programlisting>
<sect3>
<title>Simple UNION</title>
<para>
<programlisting>
tgl=> SELECT 1.2 AS Float8 UNION SELECT 1;
Float8
------
1
1.2
(2 rows)
</programlisting>
<sect3>
<title>Transposed UNION</title>
<para>
The types of the union are forced to match the types of
the first/top clause in the union:
<programlisting>
tgl=> SELECT 1 AS "All integers"
tgl-> UNION SELECT '2.2'::float4
tgl-> UNION SELECT 3.3;
All integers
------------
1
2
3
(3 rows)
</programlisting>
<para>
An alternate parser strategy could be to choose the "best" type of the bunch, but
this is more difficult because of the nice recursion technique used in the
parser. However, the "best" type is used when selecting <emphasis>into</emphasis>
a table:
<programlisting>
tgl=> CREATE TABLE ff (f float);
CREATE
tgl=> INSERT INTO ff
tgl-> SELECT 1
tgl-> UNION SELECT '2.2'::float4
tgl-> UNION SELECT 3.3;
INSERT 0 3
tgl=> SELECT f AS "Floating point" from ff;
Floating point
----------------
1
2.20000004768372
3.3
(3 rows)
</programlisting>
</chapter>

6
doc/src/sgml/user.sgml
View File

@ -11,6 +11,9 @@
<!entity environ SYSTEM "environ.sgml">
<!entity manage SYSTEM "manage.sgml">
<!entity datatype SYSTEM "datatype.sgml">
<!entity oper SYSTEM "oper.sgml">
<!entity func SYSTEM "func.sgml">
<!entity typeconv SYSTEM "typeconv.sgml">
<!entity array SYSTEM "array.sgml">
<!entity inherit SYSTEM "inherit.sgml">
<!entity query-ug SYSTEM "query-ug.sgml">
@ -92,6 +95,9 @@ It provides SQL92/SQL3 language support,
&environ;
&manage;
&datatype;
&oper;
&func;
&typeconv;
&array;
&inherit;
&query-ug;