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This module implements a data type ltree for representing labels of data stored in a hierarchical tree-like structure. Extensive facilities for searching through label trees are provided.
A label is a sequence of alphanumeric characters and underscores (for example, in C locale the characters A-Za-z0-9_ are allowed). Labels must be less than 256 bytes long.
Examples: 42, Personal_Services
A label path is a sequence of zero or more labels separated by dots, for example L1.L2.L3, representing a path from the root of a hierarchical tree to a particular node. The length of a label path must be less than 65Kb, but keeping it under 2Kb is preferable. In practice this is not a major limitation; for example, the longest label path in the DMOZ catalogue (http://www.dmoz.org) is about 240 bytes.
Example: Top.Countries.Europe.Russia
The ltree module provides several data types:
ltree stores a label path.
lquery represents a regular-expression-like pattern for matching ltree values. A simple word matches that label within a path. A star symbol (*) matches zero or more labels. For example:
foo Match the exact label path foo *.foo.* Match any label path containing the label foo *.foo Match any label path whose last label is foo
Star symbols can also be quantified to restrict how many labels they can match:
*{n} Match exactly n labels
*{n,} Match at least n labels
*{n,m} Match at least n but not more than m labels
*{,m} Match at most m labels — same as *{0,m}
There are several modifiers that can be put at the end of a non-star label in lquery to make it match more than just the exact match:
@ Match case-insensitively, for example a@ matches A * Match any label with this prefix, for example foo* matches foobar % Match initial underscore-separated words
The behavior of % is a bit complicated. It tries to match words rather than the entire label. For example foo_bar% matches foo_bar_baz but not foo_barbaz. If combined with *, prefix matching applies to each word separately, for example foo_bar%* matches foo1_bar2_baz but not foo1_br2_baz.
Also, you can write several possibly-modified labels separated with | (OR) to match any of those labels, and you can put ! (NOT) at the start to match any label that doesn't match any of the alternatives.
Here's an annotated example of lquery:
Top.*{0,2}.sport*@.!football|tennis.Russ*|Spain
a. b. c. d. e.
This query will match any label path that:
begins with the label Top
and next has zero to two labels before
a label beginning with the case-insensitive prefix sport
then a label not matching football nor tennis
and then ends with a label beginning with Russ or exactly matching Spain.
ltxtquery represents a full-text-search-like pattern for matching ltree values. An ltxtquery value contains words, possibly with the modifiers @, *, % at the end; the modifiers have the same meanings as in lquery. Words can be combined with & (AND), | (OR), ! (NOT), and parentheses. The key difference from lquery is that ltxtquery matches words without regard to their position in the label path.
Here's an example ltxtquery:
Europe & Russia*@ & !Transportation
This will match paths that contain the label Europe and any label beginning with Russia (case-insensitive), but not paths containing the label Transportation. The location of these words within the path is not important. Also, when % is used, the word can be matched to any underscore-separated word within a label, regardless of position.
Note: ltxtquery allows whitespace between symbols, but ltree and lquery do not.
Type ltree has the usual comparison operators =, <>, <, >, <=, >=. Comparison sorts in the order of a tree traversal, with the children of a node sorted by label text. In addition, there are the following specialized operators:
Table F-12. ltree Operators
| Operator | Returns | Description |
|---|---|---|
| ltree @> ltree | boolean | is left argument an ancestor of right (or equal)? |
| ltree <@ ltree | boolean | is left argument a descendant of right (or equal)? |
| ltree ~ lquery | boolean | does ltree match lquery? |
| lquery ~ ltree | boolean | does ltree match lquery? |
| ltree ? lquery[] | boolean | does ltree match any lquery in array? |
| lquery[] ? ltree | boolean | does ltree match any lquery in array? |
| ltree @ ltxtquery | boolean | does ltree match ltxtquery? |
| ltxtquery @ ltree | boolean | does ltree match ltxtquery? |
| ltree || ltree | ltree | concatenate ltree paths |
| ltree || text | ltree | convert text to ltree and concatenate |
| text || ltree | ltree | convert text to ltree and concatenate |
| ltree[] @> ltree | boolean | does array contain an ancestor of ltree? |
| ltree <@ ltree[] | boolean | does array contain an ancestor of ltree? |
| ltree[] <@ ltree | boolean | does array contain a descendant of ltree? |
| ltree @> ltree[] | boolean | does array contain a descendant of ltree? |
| ltree[] ~ lquery | boolean | does array contain any path matching lquery? |
| lquery ~ ltree[] | boolean | does array contain any path matching lquery? |
| ltree[] ? lquery[] | boolean | does ltree array contain any path matching any lquery? |
| lquery[] ? ltree[] | boolean | does ltree array contain any path matching any lquery? |
| ltree[] @ ltxtquery | boolean | does array contain any path matching ltxtquery? |
| ltxtquery @ ltree[] | boolean | does array contain any path matching ltxtquery? |
| ltree[] ?@> ltree | ltree | first array entry that is an ancestor of ltree; NULL if none |
| ltree[] ?<@ ltree | ltree | first array entry that is a descendant of ltree; NULL if none |
| ltree[] ?~ lquery | ltree | first array entry that matches lquery; NULL if none |
| ltree[] ?@ ltxtquery | ltree | first array entry that matches ltxtquery; NULL if none |
The operators <@, @>, @ and ~ have analogues ^<@, ^@>, ^@, ^~, which are the same except they do not use indexes. These are useful only for testing purposes.
The following functions are available:
Table F-13. ltree Functions
| Function | Return Type | Description | Example | Result |
|---|---|---|---|---|
subltree(ltree, int start, int end) |
ltree | subpath of ltree from position start to position end-1 (counting from 0) | subltree('Top.Child1.Child2',1,2) | Child1 |
subpath(ltree, int offset, int len) |
ltree | subpath of ltree starting at position offset, length len. If offset is negative, subpath starts that far from the end of the path. If len is negative, leaves that many labels off the end of the path. | subpath('Top.Child1.Child2',0,2) | Top.Child1 |
subpath(ltree, int offset) |
ltree | subpath of ltree starting at position offset, extending to end of path. If offset is negative, subpath starts that far from the end of the path. | subpath('Top.Child1.Child2',1) | Child1.Child2 |
nlevel(ltree) |
integer | number of labels in path | nlevel('Top.Child1.Child2') | 3 |
index(ltree a, ltree b) |
integer | position of first occurrence of b in a; -1 if not found | index('0.1.2.3.5.4.5.6.8.5.6.8','5.6') | 6 |
index(ltree a, ltree b, int offset) |
integer | position of first occurrence of b in a, searching starting at offset; negative offset means start -offset labels from the end of the path | index('0.1.2.3.5.4.5.6.8.5.6.8','5.6',-4) | 9 |
text2ltree(text) |
ltree | cast text to ltree | ||
ltree2text(ltree) |
text | cast ltree to text | ||
lca(ltree, ltree, ...) |
ltree | lowest common ancestor, i.e., longest common prefix of paths (up to 8 arguments supported) | lca('1.2.2.3','1.2.3.4.5.6') | 1.2 |
lca(ltree[]) |
ltree | lowest common ancestor, i.e., longest common prefix of paths | lca(array['1.2.2.3'::ltree,'1.2.3']) | 1.2 |
ltree supports several types of indexes that can speed up the indicated operators:
B-tree index over ltree: <, <=, =, >=, >
GiST index over ltree: <, <=, =, >=, >, @>, <@, @, ~, ?
Example of creating such an index:
CREATE INDEX path_gist_idx ON test USING GIST (path);
GiST index over ltree[]: ltree[] <@ ltree, ltree @> ltree[], @, ~, ?
Example of creating such an index:
CREATE INDEX path_gist_idx ON test USING GIST (array_path);
Note: This index type is lossy.
This example uses the following data (also available in file contrib/ltree/ltreetest.sql in the source distribution):
CREATE TABLE test (path ltree);
INSERT INTO test VALUES ('Top');
INSERT INTO test VALUES ('Top.Science');
INSERT INTO test VALUES ('Top.Science.Astronomy');
INSERT INTO test VALUES ('Top.Science.Astronomy.Astrophysics');
INSERT INTO test VALUES ('Top.Science.Astronomy.Cosmology');
INSERT INTO test VALUES ('Top.Hobbies');
INSERT INTO test VALUES ('Top.Hobbies.Amateurs_Astronomy');
INSERT INTO test VALUES ('Top.Collections');
INSERT INTO test VALUES ('Top.Collections.Pictures');
INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy');
INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy.Stars');
INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy.Galaxies');
INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy.Astronauts');
CREATE INDEX path_gist_idx ON test USING gist(path);
CREATE INDEX path_idx ON test USING btree(path);
Now, we have a table test populated with data describing the hierarchy shown below:
Top
/ | \
Science Hobbies Collections
/ | \
Astronomy Amateurs_Astronomy Pictures
/ \ |
Astrophysics Cosmology Astronomy
/ | \
Galaxies Stars Astronauts
We can do inheritance:
ltreetest=> SELECT path FROM test WHERE path <@ 'Top.Science';
path
------------------------------------
Top.Science
Top.Science.Astronomy
Top.Science.Astronomy.Astrophysics
Top.Science.Astronomy.Cosmology
(4 rows)
Here are some examples of path matching:
ltreetest=> SELECT path FROM test WHERE path ~ '*.Astronomy.*';
path
-----------------------------------------------
Top.Science.Astronomy
Top.Science.Astronomy.Astrophysics
Top.Science.Astronomy.Cosmology
Top.Collections.Pictures.Astronomy
Top.Collections.Pictures.Astronomy.Stars
Top.Collections.Pictures.Astronomy.Galaxies
Top.Collections.Pictures.Astronomy.Astronauts
(7 rows)
ltreetest=> SELECT path FROM test WHERE path ~ '*.!pictures@.*.Astronomy.*';
path
------------------------------------
Top.Science.Astronomy
Top.Science.Astronomy.Astrophysics
Top.Science.Astronomy.Cosmology
(3 rows)
Here are some examples of full text search:
ltreetest=> SELECT path FROM test WHERE path @ 'Astro*% & !pictures@';
path
------------------------------------
Top.Science.Astronomy
Top.Science.Astronomy.Astrophysics
Top.Science.Astronomy.Cosmology
Top.Hobbies.Amateurs_Astronomy
(4 rows)
ltreetest=> SELECT path FROM test WHERE path @ 'Astro* & !pictures@';
path
------------------------------------
Top.Science.Astronomy
Top.Science.Astronomy.Astrophysics
Top.Science.Astronomy.Cosmology
(3 rows)
Path construction using functions:
ltreetest=> SELECT subpath(path,0,2)||'Space'||subpath(path,2) FROM test WHERE path <@ 'Top.Science.Astronomy';
?column?
------------------------------------------
Top.Science.Space.Astronomy
Top.Science.Space.Astronomy.Astrophysics
Top.Science.Space.Astronomy.Cosmology
(3 rows)
We could simplify this by creating a SQL function that inserts a label at a specified position in a path:
CREATE FUNCTION ins_label(ltree, int, text) RETURNS ltree
AS 'select subpath($1,0,$2) || $3 || subpath($1,$2);'
LANGUAGE SQL IMMUTABLE;
ltreetest=> SELECT ins_label(path,2,'Space') FROM test WHERE path <@ 'Top.Science.Astronomy';
ins_label
------------------------------------------
Top.Science.Space.Astronomy
Top.Science.Space.Astronomy.Astrophysics
Top.Science.Space.Astronomy.Cosmology
(3 rows)
All work was done by Teodor Sigaev (<teodor@stack.net>) and
Oleg Bartunov (<oleg@sai.msu.su>). See
http://www.sai.msu.su/~megera/postgres/gist/ for
additional information. Authors would like to thank Eugeny Rodichev for
helpful discussions. Comments and bug reports are welcome.