F.8. btree_gist - GiST operator classes with B-tree behavior
btree_gist
provides GiST index operator classes that
implement B-tree equivalent behavior for the data types
int2
,
int4
,
int8
,
float4
,
float8
,
numeric
,
timestamp with time zone
,
timestamp without time zone
,
time with time zone
,
time without time zone
,
date
,
interval
,
oid
,
money
,
char
,
varchar
,
text
,
bytea
,
bit
,
varbit
,
macaddr
,
macaddr8
,
inet
,
cidr
,
uuid
,
bool
and all
enum
types.
In general, these operator classes will not outperform the equivalent standard B-tree index methods, and they lack one major feature of the standard B-tree code: the ability to enforce uniqueness. However, they provide some other features that are not available with a B-tree index, as described below. Also, these operator classes are useful when a multicolumn GiST index is needed, wherein some of the columns are of data types that are only indexable with GiST but other columns are just simple data types. Lastly, these operator classes are useful for GiST testing and as a base for developing other GiST operator classes.
In addition to the typical B-tree search operators,
btree_gist
also provides index support for
<>
(
"
not
equals
"
). This may be useful in combination with an
exclusion constraint
,
as described below.
Also, for data types for which there is a natural distance metric,
btree_gist
defines a distance operator
<->
,
and provides GiST index support for nearest-neighbor searches using
this operator. Distance operators are provided for
int2
,
int4
,
int8
,
float4
,
float8
,
timestamp with time zone
,
timestamp without time zone
,
time without time zone
,
date
,
interval
,
oid
, and
money
.
This module is considered
"
trusted
"
, that is, it can be
installed by non-superusers who have
CREATE
privilege
on the current database.
F.8.1. Example Usage #
Simple example using
btree_gist
instead of
btree
:
CREATE TABLE test (a int4); -- create index CREATE INDEX testidx ON test USING GIST (a); -- query SELECT * FROM test WHERE a < 10; -- nearest-neighbor search: find the ten entries closest to "42" SELECT *, a <-> 42 AS dist FROM test ORDER BY a <-> 42 LIMIT 10;
Use an exclusion constraint to enforce the rule that a cage at a zoo can contain only one kind of animal:
=> CREATE TABLE zoo ( cage INTEGER, animal TEXT, EXCLUDE USING GIST (cage WITH =, animal WITH <>) ); => INSERT INTO zoo VALUES(123, 'zebra'); INSERT 0 1 => INSERT INTO zoo VALUES(123, 'zebra'); INSERT 0 1 => INSERT INTO zoo VALUES(123, 'lion'); ERROR: conflicting key value violates exclusion constraint "zoo_cage_animal_excl" DETAIL: Key (cage, animal)=(123, lion) conflicts with existing key (cage, animal)=(123, zebra). => INSERT INTO zoo VALUES(124, 'lion'); INSERT 0 1
F.8.2. Authors #
Teodor Sigaev (
<
teodor@stack.net
>
),
Oleg Bartunov (
<
oleg@sai.msu.su
>
),
Janko Richter (
<
jankorichter@yahoo.de
>
), and
Paul Jungwirth (
<
pj@illuminatedcomputing.com
>
). See
http://www.sai.msu.su/~megera/postgres/gist/
for additional information.