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<!-- manual page source format generated by PolyglotMan v3.0.4, -->
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<HTML>
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<TITLE>"CREATE(INDEX") manual page</TITLE>
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<A HREF="sql.html">SQL Reference Contents</A>
<H2><A NAME="sect0" HREF="#toc0">NAME </A></H2>
create index - construct a secondary index
<H2><A NAME="sect1" HREF="#toc1">SYNOPSIS </A></H2>
<B>create </B> [<B>unique
</B>] <B>index </B> index-name <BR>
<tt> </tt><tt> </tt><B>on </B> classname [<B>using </B> am-name] <BR>
<tt> </tt><tt> </tt><B>( </B> attname [type_class],
...<B> ) </B> <BR>
<P>
<B>create </B> [<B>unique </B>] <B>index </B> index-name <BR>
<tt> </tt><tt> </tt><B>on </B> classname [<B>using </B> am-name]
<BR>
<tt> </tt><tt> </tt><B>( </B> funcname <B>( </B> attname-1 { , attname-i } <B>) </B> type_class <B>) </B> <BR>
<H2><A NAME="sect2" HREF="#toc2">DESCRIPTION
</A></H2>
This command constructs an index called <I>index-name.</I> <P>
<I>Am-name</I> is the name of
the access method which is used for the index. The default access method
is btree. <P>
In the first syntax shown above, the key fields for the index
are specified as attribute names. It may also have an associated <I>operator
class</I>. An operator class is used to specify the operators to be used for
a particular index. For example, a btree index on four-byte integers would
use the <I>int4_ops</I> class; this operator class includes comparison functions
for four-byte integers. The default operator class is the appropriate operator
class for that field type. <P>
<B>Note: </B> currently, only <I>btree</I> access method
supports multi-attribute indices. Up to 7 keys may be specified. <P>
In the second
syntax shown above, an index can be defined on the result of a user-defined
function <I>funcname</I> applied to one or more attributes of a single class.
These <I>functional indices</I> can be used to obtain fast access to data based
on operators that would normally require some transformation to be applied
to the base data. For example, say you have an attribute in class `myclass'
called `pt' that consists of a 2D point type. Now, suppose that you would
like to index this attribute but you only have index operator classes
for 2D polygon types. You can define an index on the point attribute using
a function that you write (call it `point_to_polygon') and your existing
polygon operator class; after that, queries using existing polygon operators
that reference `point_to_polygon(myclass.pt)' on one side will use the precomputed
polygons stored in the functional index instead of computing a polygon
for each and every instance in `myclass' and then comparing it to the value
on the other side of the operator. Obviously, the decision to build a functional
index represents a tradeoff between space (for the index) and execution
time. <P>
The <B>unique </B> keyword causes the system to check for duplicate values
when the index is created (if data already exist) and each time data is
added. Attempts to insert or update non-duplicate data will generate an
error. <P>
Postgres provides btree, rtree and hash access methods for secondary
indices. The btree access method is an implementation of the Lehman-Yao
high-concurrency btrees. The rtree access method implements standard rtrees
using Guttman's quadratic split algorithm. The hash access method is an
implementation of Litwin's linear hashing. We mention the algorithms used
solely to indicate that all of these access methods are fully dynamic
and do not have to be optimized periodically (as is the case with, for
example, static hash access methods). <P>
This list was generated from the
Postgres system catalogs with the query: <P>
SELECT am.amname AS acc_name,
<BR>
opc.opcname AS ops_name, <BR>
opr.oprname AS ops_comp <BR>
FROM
pg_am am, pg_amop amop, pg_opclass opc, pg_operator opr <BR>
WHERE amop.amopid
= am.oid AND <BR>
amop.amopclaid = opc.oid AND <BR>
amop.amopopr = opr.oid
<BR>
ORDER BY acc_name, ops_name, ops_comp; <BR>
<P>
acc_name|ops_name |ops_comp
<BR>
--------+-----------+-------- <BR>
btree |abstime_ops|< <BR>
btree |abstime_ops|<= <BR>
btree |abstime_ops|=
<BR>
btree |abstime_ops|> <BR>
btree |abstime_ops|>= <BR>
btree
|bpchar_ops |< <BR>
btree |bpchar_ops |<= <BR>
btree |bpchar_ops |=
<BR>
btree |bpchar_ops |> <BR>
btree |bpchar_ops |>= <BR>
btree
|char16_ops |< <BR>
btree |char16_ops |<= <BR>
btree |char16_ops |=
<BR>
btree |char16_ops |> <BR>
btree |char16_ops |>= <BR>
btree
|char2_ops |< <BR>
btree |char2_ops |<= <BR>
btree |char2_ops |=
<BR>
btree |char2_ops |> <BR>
btree |char2_ops |>= <BR>
btree
|char4_ops |< <BR>
btree |char4_ops |<= <BR>
btree |char4_ops |=
<BR>
btree |char4_ops |> <BR>
btree |char4_ops |>= <BR>
btree
|char8_ops |< <BR>
btree |char8_ops |<= <BR>
btree |char8_ops |=
<BR>
btree |char8_ops |> <BR>
btree |char8_ops |>= <BR>
btree
|char_ops |< <BR>
btree |char_ops |<= <BR>
btree |char_ops |=
<BR>
btree |char_ops |> <BR>
btree |char_ops |>= <BR>
btree
|date_ops |< <BR>
btree |date_ops |<= <BR>
btree |date_ops |=
<BR>
btree |date_ops |> <BR>
btree |date_ops |>= <BR>
btree
|float4_ops |< <BR>
btree |float4_ops |<= <BR>
btree |float4_ops |=
<BR>
btree |float4_ops |> <BR>
btree |float4_ops |>= <BR>
btree
|float8_ops |< <BR>
btree |float8_ops |<= <BR>
btree |float8_ops |=
<BR>
btree |float8_ops |> <BR>
btree |float8_ops |>= <BR>
btree
|int24_ops |< <BR>
btree |int24_ops |<= <BR>
btree |int24_ops |=
<BR>
btree |int24_ops |> <BR>
btree |int24_ops |>= <BR>
btree
|int2_ops |< <BR>
btree |int2_ops |<= <BR>
btree |int2_ops |=
<BR>
btree |int2_ops |> <BR>
btree |int2_ops |>= <BR>
btree
|int42_ops |< <BR>
btree |int42_ops |<= <BR>
btree |int42_ops |=
<BR>
btree |int42_ops |> <BR>
btree |int42_ops |>= <BR>
btree
|int4_ops |< <BR>
btree |int4_ops |<= <BR>
btree |int4_ops |=
<BR>
btree |int4_ops |> <BR>
btree |int4_ops |>= <BR>
btree
|name_ops |< <BR>
btree |name_ops |<= <BR>
btree |name_ops |=
<BR>
btree |name_ops |> <BR>
btree |name_ops |>= <BR>
btree
|oid_ops |< <BR>
btree |oid_ops |<= <BR>
btree |oid_ops |=
<BR>
btree |oid_ops |> <BR>
btree |oid_ops |>= <BR>
btree
|oidint2_ops|< <BR>
btree |oidint2_ops|<= <BR>
btree |oidint2_ops|=
<BR>
btree |oidint2_ops|> <BR>
btree |oidint2_ops|>= <BR>
btree
|oidint4_ops|< <BR>
btree |oidint4_ops|<= <BR>
btree |oidint4_ops|=
<BR>
btree |oidint4_ops|> <BR>
btree |oidint4_ops|>= <BR>
btree
|oidname_ops|< <BR>
btree |oidname_ops|<= <BR>
btree |oidname_ops|=
<BR>
btree |oidname_ops|> <BR>
btree |oidname_ops|>= <BR>
btree
|text_ops |< <BR>
btree |text_ops |<= <BR>
btree |text_ops |=
<BR>
btree |text_ops |> <BR>
btree |text_ops |>= <BR>
btree
|time_ops |< <BR>
btree |time_ops |<= <BR>
btree |time_ops |=
<BR>
btree |time_ops |> <BR>
btree |time_ops |>= <BR>
btree
|varchar_ops|< <BR>
btree |varchar_ops|<= <BR>
btree |varchar_ops|=
<BR>
btree |varchar_ops|> <BR>
btree |varchar_ops|>= <BR>
hash
|bpchar_ops |= <BR>
hash |char16_ops |= <BR>
hash |char2_ops
|= <BR>
hash |char4_ops |= <BR>
hash |char8_ops |= <BR>
hash
|char_ops |= <BR>
hash |date_ops |= <BR>
hash |float4_ops
|= <BR>
hash |float8_ops |= <BR>
hash |int2_ops |= <BR>
hash
|int4_ops |= <BR>
hash |name_ops |= <BR>
hash |oid_ops
|= <BR>
hash |text_ops |= <BR>
hash |time_ops |= <BR>
hash |varchar_ops|= <BR>
rtree |bigbox_ops |&& <BR>
rtree |bigbox_ops
|&< <BR>
rtree |bigbox_ops |&> <BR>
rtree |bigbox_ops |<< <BR>
rtree
|bigbox_ops |>> <BR>
rtree |bigbox_ops |@ <BR>
rtree |bigbox_ops |~
<BR>
rtree |bigbox_ops |~= <BR>
rtree |box_ops |&& <BR>
rtree
|box_ops |&< <BR>
rtree |box_ops |&> <BR>
rtree |box_ops |<<
<BR>
rtree |box_ops |>> <BR>
rtree |box_ops |@ <BR>
rtree |box_ops
|~ <BR>
rtree |box_ops |~= <BR>
rtree |poly_ops |&& <BR>
rtree
|poly_ops |&< <BR>
rtree |poly_ops |&> <BR>
rtree |poly_ops |<<
<BR>
rtree |poly_ops |>> <BR>
rtree |poly_ops |@ <BR>
rtree |poly_ops
|~ <BR>
rtree |poly_ops |~= <BR>
<P>
The <I>int24_ops</I> operator class
is useful for constructing indices on int2 data, and doing comparisons
against int4 data in query qualifications. Similarly, <I>int42_ops</I> support
indices on int4 data that is to be compared against int2 data in queries.
<P>
The operator classes <I>oidint2_ops</I>, <I>oidint4_ops</I>, and <I>oidchar16_ops</I> represent
the use of <I>functional indices</I> to simulate multi-key indices. These are
no longer needed now that multi-key indexes are supported. <P>
The Postgres
query optimizer will consider using btree indices in a scan whenever an
indexed attribute is involved in a comparison using one of: <P>
< <=
= >= > <BR>
<P>
Both box classes support indices on the `box' datatype in Postgres.
The difference between them is that <I>bigbox_ops</I> scales box coordinates
down, to avoid floating point exceptions from doing multiplication, addition,
and subtraction on very large floating-point coordinates. If the field
on which your rectangles lie is about 20,000 units square or larger, you
should use <I>bigbox_ops</I>. The <I>poly_ops</I> operator class supports rtree indices
on `polygon' data. <P>
The Postgres query optimizer will consider using an rtree
index whenever an indexed attribute is involved in a comparison using
one of: <P>
<< &< &> >> @ ~= && <BR>
<P>
The Postgres query optimizer will
consider using a hash index whenever an indexed attribute is involved
in a comparison using the <B>= </B> operator.
<H2><A NAME="sect3" HREF="#toc3">EXAMPLES </A></H2>
-- <BR>
--Create a btree index
on the emp class using the age attribute. <BR>
-- <BR>
create index empindex on emp
using btree (age int4_ops) <BR>
-- <BR>
--Create a btree index on employee name. <BR>
--
<BR>
create index empname <BR>
<tt> </tt><tt> </tt>on emp using btree (name char16_ops) <BR>
-- <BR>
--Create
an rtree index on the bounding rectangle of cities. <BR>
-- <BR>
create index cityrect
<BR>
<tt> </tt><tt> </tt>on city using rtree (boundbox box_ops) <BR>
-- <BR>
--Create a rtree index on a point
attribute such that we <BR>
--can efficiently use box operators on the result
of the <BR>
--conversion function. Such a qualification might look <BR>
--like "where
point2box(points.pointloc) = boxes.box". <BR>
-- <BR>
create index pointloc <BR>
<tt> </tt><tt> </tt>on points
using rtree (<A HREF="point2box.location.html">point2box(location)</A>
box_ops) <BR>
<P>
<HR><P>
<A NAME="toc"><B>Table of Contents</B></A><P>
<UL>
<LI><A NAME="toc0" HREF="#sect0">NAME</A></LI>
<LI><A NAME="toc1" HREF="#sect1">SYNOPSIS</A></LI>
<LI><A NAME="toc2" HREF="#sect2">DESCRIPTION</A></LI>
<LI><A NAME="toc3" HREF="#sect3">EXAMPLES</A></LI>
</UL>
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