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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>F.23. ltree — hierarchical tree-like data type</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="lo.html" title="F.22. lo — manage large objects" /><link rel="next" href="oldsnapshot.html" title="F.24. old_snapshot — inspect old_snapshot_threshold state" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.23. ltree — hierarchical tree-like data type</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="lo.html" title="F.22. lo — manage large objects">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules and Extensions</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="oldsnapshot.html" title="F.24. old_snapshot — inspect old_snapshot_threshold state">Next</a></td></tr></table><hr /></div><div class="sect1" id="LTREE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.23. ltree — hierarchical tree-like data type <a href="#LTREE" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="ltree.html#LTREE-DEFINITIONS">F.23.1. Definitions</a></span></dt><dt><span class="sect2"><a href="ltree.html#LTREE-OPS-FUNCS">F.23.2. Operators and Functions</a></span></dt><dt><span class="sect2"><a href="ltree.html#LTREE-INDEXES">F.23.3. Indexes</a></span></dt><dt><span class="sect2"><a href="ltree.html#LTREE-EXAMPLE">F.23.4. Example</a></span></dt><dt><span class="sect2"><a href="ltree.html#LTREE-TRANSFORMS">F.23.5. Transforms</a></span></dt><dt><span class="sect2"><a href="ltree.html#LTREE-AUTHORS">F.23.6. Authors</a></span></dt></dl></div><a id="id-1.11.7.33.2" class="indexterm"></a><p>
This module implements a data type <code class="type">ltree</code> for representing
labels of data stored in a hierarchical tree-like structure.
Extensive facilities for searching through label trees are provided.
</p><p>
This module is considered <span class="quote">“<span class="quote">trusted</span>”</span>, that is, it can be
installed by non-superusers who have <code class="literal">CREATE</code> privilege
on the current database.
</p><div class="sect2" id="LTREE-DEFINITIONS"><div class="titlepage"><div><div><h3 class="title">F.23.1. Definitions <a href="#LTREE-DEFINITIONS" class="id_link">#</a></h3></div></div></div><p>
A <em class="firstterm">label</em> is a sequence of alphanumeric characters,
underscores, and hyphens. Valid alphanumeric character ranges are
dependent on the database locale. For example, in C locale, the characters
<code class="literal">A-Za-z0-9_-</code> are allowed.
Labels must be no more than 1000 characters long.
</p><p>
Examples: <code class="literal">42</code>, <code class="literal">Personal_Services</code>
</p><p>
A <em class="firstterm">label path</em> is a sequence of zero or more
labels separated by dots, for example <code class="literal">L1.L2.L3</code>, representing
a path from the root of a hierarchical tree to a particular node. The
length of a label path cannot exceed 65535 labels.
</p><p>
Example: <code class="literal">Top.Countries.Europe.Russia</code>
</p><p>
The <code class="filename">ltree</code> module provides several data types:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
<code class="type">ltree</code> stores a label path.
</p></li><li class="listitem"><p>
<code class="type">lquery</code> represents a regular-expression-like pattern
for matching <code class="type">ltree</code> values. A simple word matches that
label within a path. A star symbol (<code class="literal">*</code>) matches zero
or more labels. These can be joined with dots to form a pattern that
must match the whole label path. For example:
</p><pre class="synopsis">
foo <em class="lineannotation"><span class="lineannotation">Match the exact label path <code class="literal">foo</code></span></em>
*.foo.* <em class="lineannotation"><span class="lineannotation">Match any label path containing the label <code class="literal">foo</code></span></em>
*.foo <em class="lineannotation"><span class="lineannotation">Match any label path whose last label is <code class="literal">foo</code></span></em>
</pre><p>
</p><p>
Both star symbols and simple words can be quantified to restrict how many
labels they can match:
</p><pre class="synopsis">
*{<em class="replaceable"><code>n</code></em>} <em class="lineannotation"><span class="lineannotation">Match exactly <em class="replaceable"><code>n</code></em> labels</span></em>
*{<em class="replaceable"><code>n</code></em>,} <em class="lineannotation"><span class="lineannotation">Match at least <em class="replaceable"><code>n</code></em> labels</span></em>
*{<em class="replaceable"><code>n</code></em>,<em class="replaceable"><code>m</code></em>} <em class="lineannotation"><span class="lineannotation">Match at least <em class="replaceable"><code>n</code></em> but not more than <em class="replaceable"><code>m</code></em> labels</span></em>
*{,<em class="replaceable"><code>m</code></em>} <em class="lineannotation"><span class="lineannotation">Match at most <em class="replaceable"><code>m</code></em> labels — same as </span></em>*{0,<em class="replaceable"><code>m</code></em>}
foo{<em class="replaceable"><code>n</code></em>,<em class="replaceable"><code>m</code></em>} <em class="lineannotation"><span class="lineannotation">Match at least <em class="replaceable"><code>n</code></em> but not more than <em class="replaceable"><code>m</code></em> occurrences of <code class="literal">foo</code></span></em>
foo{,} <em class="lineannotation"><span class="lineannotation">Match any number of occurrences of <code class="literal">foo</code>, including zero</span></em>
</pre><p>
In the absence of any explicit quantifier, the default for a star symbol
is to match any number of labels (that is, <code class="literal">{,}</code>) while
the default for a non-star item is to match exactly once (that
is, <code class="literal">{1}</code>).
</p><p>
There are several modifiers that can be put at the end of a non-star
<code class="type">lquery</code> item to make it match more than just the exact match:
</p><pre class="synopsis">
@ <em class="lineannotation"><span class="lineannotation">Match case-insensitively, for example <code class="literal">a@</code> matches <code class="literal">A</code></span></em>
* <em class="lineannotation"><span class="lineannotation">Match any label with this prefix, for example <code class="literal">foo*</code> matches <code class="literal">foobar</code></span></em>
% <em class="lineannotation"><span class="lineannotation">Match initial underscore-separated words</span></em>
</pre><p>
The behavior of <code class="literal">%</code> is a bit complicated. It tries to match
words rather than the entire label. For example
<code class="literal">foo_bar%</code> matches <code class="literal">foo_bar_baz</code> but not
<code class="literal">foo_barbaz</code>. If combined with <code class="literal">*</code>, prefix
matching applies to each word separately, for example
<code class="literal">foo_bar%*</code> matches <code class="literal">foo1_bar2_baz</code> but
not <code class="literal">foo1_br2_baz</code>.
</p><p>
Also, you can write several possibly-modified non-star items separated with
<code class="literal">|</code> (OR) to match any of those items, and you can put
<code class="literal">!</code> (NOT) at the start of a non-star group to match any
label that doesn't match any of the alternatives. A quantifier, if any,
goes at the end of the group; it means some number of matches for the
group as a whole (that is, some number of labels matching or not matching
any of the alternatives).
</p><p>
Here's an annotated example of <code class="type">lquery</code>:
</p><pre class="programlisting">
Top.*{0,2}.sport*@.!football|tennis{1,}.Russ*|Spain
a. b. c. d. e.
</pre><p>
This query will match any label path that:
</p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><p>
begins with the label <code class="literal">Top</code>
</p></li><li class="listitem"><p>
and next has zero to two labels before
</p></li><li class="listitem"><p>
a label beginning with the case-insensitive prefix <code class="literal">sport</code>
</p></li><li class="listitem"><p>
then has one or more labels, none of which
match <code class="literal">football</code> nor <code class="literal">tennis</code>
</p></li><li class="listitem"><p>
and then ends with a label beginning with <code class="literal">Russ</code> or
exactly matching <code class="literal">Spain</code>.
</p></li></ol></div></li><li class="listitem"><p><code class="type">ltxtquery</code> represents a full-text-search-like
pattern for matching <code class="type">ltree</code> values. An
<code class="type">ltxtquery</code> value contains words, possibly with the
modifiers <code class="literal">@</code>, <code class="literal">*</code>, <code class="literal">%</code> at the end;
the modifiers have the same meanings as in <code class="type">lquery</code>.
Words can be combined with <code class="literal">&</code> (AND),
<code class="literal">|</code> (OR), <code class="literal">!</code> (NOT), and parentheses.
The key difference from
<code class="type">lquery</code> is that <code class="type">ltxtquery</code> matches words without
regard to their position in the label path.
</p><p>
Here's an example <code class="type">ltxtquery</code>:
</p><pre class="programlisting">
Europe & Russia*@ & !Transportation
</pre><p>
This will match paths that contain the label <code class="literal">Europe</code> and
any label beginning with <code class="literal">Russia</code> (case-insensitive),
but not paths containing the label <code class="literal">Transportation</code>.
The location of these words within the path is not important.
Also, when <code class="literal">%</code> is used, the word can be matched to any
underscore-separated word within a label, regardless of position.
</p></li></ul></div><p>
Note: <code class="type">ltxtquery</code> allows whitespace between symbols, but
<code class="type">ltree</code> and <code class="type">lquery</code> do not.
</p></div><div class="sect2" id="LTREE-OPS-FUNCS"><div class="titlepage"><div><div><h3 class="title">F.23.2. Operators and Functions <a href="#LTREE-OPS-FUNCS" class="id_link">#</a></h3></div></div></div><p>
Type <code class="type">ltree</code> has the usual comparison operators
<code class="literal">=</code>, <code class="literal"><></code>,
<code class="literal"><</code>, <code class="literal">></code>, <code class="literal"><=</code>, <code class="literal">>=</code>.
Comparison sorts in the order of a tree traversal, with the children
of a node sorted by label text. In addition, the specialized
operators shown in <a class="xref" href="ltree.html#LTREE-OP-TABLE" title="Table F.13. ltree Operators">Table F.13</a> are available.
</p><div class="table" id="LTREE-OP-TABLE"><p class="title"><strong>Table F.13. <code class="type">ltree</code> Operators</strong></p><div class="table-contents"><table class="table" summary="ltree Operators" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Operator
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree</code> <code class="literal">@></code> <code class="type">ltree</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Is left argument an ancestor of right (or equal)?
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree</code> <code class="literal"><@</code> <code class="type">ltree</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Is left argument a descendant of right (or equal)?
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree</code> <code class="literal">~</code> <code class="type">lquery</code>
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="type">lquery</code> <code class="literal">~</code> <code class="type">ltree</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Does <code class="type">ltree</code> match <code class="type">lquery</code>?
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree</code> <code class="literal">?</code> <code class="type">lquery[]</code>
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="type">lquery[]</code> <code class="literal">?</code> <code class="type">ltree</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Does <code class="type">ltree</code> match any <code class="type">lquery</code> in array?
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree</code> <code class="literal">@</code> <code class="type">ltxtquery</code>
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="type">ltxtquery</code> <code class="literal">@</code> <code class="type">ltree</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Does <code class="type">ltree</code> match <code class="type">ltxtquery</code>?
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree</code> <code class="literal">||</code> <code class="type">ltree</code>
→ <code class="returnvalue">ltree</code>
</p>
<p>
Concatenates <code class="type">ltree</code> paths.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree</code> <code class="literal">||</code> <code class="type">text</code>
→ <code class="returnvalue">ltree</code>
</p>
<p class="func_signature">
<code class="type">text</code> <code class="literal">||</code> <code class="type">ltree</code>
→ <code class="returnvalue">ltree</code>
</p>
<p>
Converts text to <code class="type">ltree</code> and concatenates.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree[]</code> <code class="literal">@></code> <code class="type">ltree</code>
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="type">ltree</code> <code class="literal"><@</code> <code class="type">ltree[]</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Does array contain an ancestor of <code class="type">ltree</code>?
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree[]</code> <code class="literal"><@</code> <code class="type">ltree</code>
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="type">ltree</code> <code class="literal">@></code> <code class="type">ltree[]</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Does array contain a descendant of <code class="type">ltree</code>?
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree[]</code> <code class="literal">~</code> <code class="type">lquery</code>
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="type">lquery</code> <code class="literal">~</code> <code class="type">ltree[]</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Does array contain any path matching <code class="type">lquery</code>?
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree[]</code> <code class="literal">?</code> <code class="type">lquery[]</code>
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="type">lquery[]</code> <code class="literal">?</code> <code class="type">ltree[]</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Does <code class="type">ltree</code> array contain any path matching
any <code class="type">lquery</code>?
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree[]</code> <code class="literal">@</code> <code class="type">ltxtquery</code>
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="type">ltxtquery</code> <code class="literal">@</code> <code class="type">ltree[]</code>
→ <code class="returnvalue">boolean</code>
</p>
<p>
Does array contain any path matching <code class="type">ltxtquery</code>?
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree[]</code> <code class="literal">?@></code> <code class="type">ltree</code>
→ <code class="returnvalue">ltree</code>
</p>
<p>
Returns first array entry that is an ancestor of <code class="type">ltree</code>,
or <code class="literal">NULL</code> if none.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree[]</code> <code class="literal">?<@</code> <code class="type">ltree</code>
→ <code class="returnvalue">ltree</code>
</p>
<p>
Returns first array entry that is a descendant of <code class="type">ltree</code>,
or <code class="literal">NULL</code> if none.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree[]</code> <code class="literal">?~</code> <code class="type">lquery</code>
→ <code class="returnvalue">ltree</code>
</p>
<p>
Returns first array entry that matches <code class="type">lquery</code>,
or <code class="literal">NULL</code> if none.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="type">ltree[]</code> <code class="literal">?@</code> <code class="type">ltxtquery</code>
→ <code class="returnvalue">ltree</code>
</p>
<p>
Returns first array entry that matches <code class="type">ltxtquery</code>,
or <code class="literal">NULL</code> if none.
</p></td></tr></tbody></table></div></div><br class="table-break" /><p>
The operators <code class="literal"><@</code>, <code class="literal">@></code>,
<code class="literal">@</code> and <code class="literal">~</code> have analogues
<code class="literal">^<@</code>, <code class="literal">^@></code>, <code class="literal">^@</code>,
<code class="literal">^~</code>, which are the same except they do not use
indexes. These are useful only for testing purposes.
</p><p>
The available functions are shown in <a class="xref" href="ltree.html#LTREE-FUNC-TABLE" title="Table F.14. ltree Functions">Table F.14</a>.
</p><div class="table" id="LTREE-FUNC-TABLE"><p class="title"><strong>Table F.14. <code class="type">ltree</code> Functions</strong></p><div class="table-contents"><table class="table" summary="ltree Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p>
<p>
Example(s)
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.33.6.6.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">subltree</code> ( <code class="type">ltree</code>, <em class="parameter"><code>start</code></em> <code class="type">integer</code>, <em class="parameter"><code>end</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">ltree</code>
</p>
<p>
Returns subpath of <code class="type">ltree</code> from
position <em class="parameter"><code>start</code></em> to
position <em class="parameter"><code>end</code></em>-1 (counting from 0).
</p>
<p>
<code class="literal">subltree('Top.Child1.Child2', 1, 2)</code>
→ <code class="returnvalue">Child1</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.33.6.6.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">subpath</code> ( <code class="type">ltree</code>, <em class="parameter"><code>offset</code></em> <code class="type">integer</code>, <em class="parameter"><code>len</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">ltree</code>
</p>
<p>
Returns subpath of <code class="type">ltree</code> starting at
position <em class="parameter"><code>offset</code></em>, with
length <em class="parameter"><code>len</code></em>. If <em class="parameter"><code>offset</code></em>
is negative, subpath starts that far from the end of the path.
If <em class="parameter"><code>len</code></em> is negative, leaves that many labels off
the end of the path.
</p>
<p>
<code class="literal">subpath('Top.Child1.Child2', 0, 2)</code>
→ <code class="returnvalue">Top.Child1</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="function">subpath</code> ( <code class="type">ltree</code>, <em class="parameter"><code>offset</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">ltree</code>
</p>
<p>
Returns subpath of <code class="type">ltree</code> starting at
position <em class="parameter"><code>offset</code></em>, extending to end of path.
If <em class="parameter"><code>offset</code></em> is negative, subpath starts that far
from the end of the path.
</p>
<p>
<code class="literal">subpath('Top.Child1.Child2', 1)</code>
→ <code class="returnvalue">Child1.Child2</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.33.6.6.2.2.4.1.1.1" class="indexterm"></a>
<code class="function">nlevel</code> ( <code class="type">ltree</code> )
→ <code class="returnvalue">integer</code>
</p>
<p>
Returns number of labels in path.
</p>
<p>
<code class="literal">nlevel('Top.Child1.Child2')</code>
→ <code class="returnvalue">3</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.33.6.6.2.2.5.1.1.1" class="indexterm"></a>
<code class="function">index</code> ( <em class="parameter"><code>a</code></em> <code class="type">ltree</code>, <em class="parameter"><code>b</code></em> <code class="type">ltree</code> )
→ <code class="returnvalue">integer</code>
</p>
<p>
Returns position of first occurrence of <em class="parameter"><code>b</code></em> in
<em class="parameter"><code>a</code></em>, or -1 if not found.
</p>
<p>
<code class="literal">index('0.1.2.3.5.4.5.6.8.5.6.8', '5.6')</code>
→ <code class="returnvalue">6</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="function">index</code> ( <em class="parameter"><code>a</code></em> <code class="type">ltree</code>, <em class="parameter"><code>b</code></em> <code class="type">ltree</code>, <em class="parameter"><code>offset</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">integer</code>
</p>
<p>
Returns position of first occurrence of <em class="parameter"><code>b</code></em>
in <em class="parameter"><code>a</code></em>, or -1 if not found. The search starts at
position <em class="parameter"><code>offset</code></em>;
negative <em class="parameter"><code>offset</code></em> means
start <em class="parameter"><code>-offset</code></em> labels from the end of the path.
</p>
<p>
<code class="literal">index('0.1.2.3.5.4.5.6.8.5.6.8', '5.6', -4)</code>
→ <code class="returnvalue">9</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.33.6.6.2.2.7.1.1.1" class="indexterm"></a>
<code class="function">text2ltree</code> ( <code class="type">text</code> )
→ <code class="returnvalue">ltree</code>
</p>
<p>
Casts <code class="type">text</code> to <code class="type">ltree</code>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.33.6.6.2.2.8.1.1.1" class="indexterm"></a>
<code class="function">ltree2text</code> ( <code class="type">ltree</code> )
→ <code class="returnvalue">text</code>
</p>
<p>
Casts <code class="type">ltree</code> to <code class="type">text</code>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.11.7.33.6.6.2.2.9.1.1.1" class="indexterm"></a>
<code class="function">lca</code> ( <code class="type">ltree</code> [<span class="optional">, <code class="type">ltree</code> [<span class="optional">, ... </span>]</span>] )
→ <code class="returnvalue">ltree</code>
</p>
<p>
Computes longest common ancestor of paths
(up to 8 arguments are supported).
</p>
<p>
<code class="literal">lca('1.2.3', '1.2.3.4.5.6')</code>
→ <code class="returnvalue">1.2</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<code class="function">lca</code> ( <code class="type">ltree[]</code> )
→ <code class="returnvalue">ltree</code>
</p>
<p>
Computes longest common ancestor of paths in array.
</p>
<p>
<code class="literal">lca(array['1.2.3'::ltree,'1.2.3.4'])</code>
→ <code class="returnvalue">1.2</code>
</p></td></tr></tbody></table></div></div><br class="table-break" /></div><div class="sect2" id="LTREE-INDEXES"><div class="titlepage"><div><div><h3 class="title">F.23.3. Indexes <a href="#LTREE-INDEXES" class="id_link">#</a></h3></div></div></div><p>
<code class="filename">ltree</code> supports several types of indexes that can speed
up the indicated operators:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
B-tree index over <code class="type">ltree</code>:
<code class="literal"><</code>, <code class="literal"><=</code>, <code class="literal">=</code>,
<code class="literal">>=</code>, <code class="literal">></code>
</p></li><li class="listitem"><p>
GiST index over <code class="type">ltree</code> (<code class="literal">gist_ltree_ops</code>
opclass):
<code class="literal"><</code>, <code class="literal"><=</code>, <code class="literal">=</code>,
<code class="literal">>=</code>, <code class="literal">></code>,
<code class="literal">@></code>, <code class="literal"><@</code>,
<code class="literal">@</code>, <code class="literal">~</code>, <code class="literal">?</code>
</p><p>
<code class="literal">gist_ltree_ops</code> GiST opclass approximates a set of
path labels as a bitmap signature. Its optional integer parameter
<code class="literal">siglen</code> determines the
signature length in bytes. The default signature length is 8 bytes.
The length must be a positive multiple of <code class="type">int</code> alignment
(4 bytes on most machines)) up to 2024. Longer
signatures lead to a more precise search (scanning a smaller fraction of the index and
fewer heap pages), at the cost of a larger index.
</p><p>
Example of creating such an index with the default signature length of 8 bytes:
</p><pre class="programlisting">
CREATE INDEX path_gist_idx ON test USING GIST (path);
</pre><p>
Example of creating such an index with a signature length of 100 bytes:
</p><pre class="programlisting">
CREATE INDEX path_gist_idx ON test USING GIST (path gist_ltree_ops(siglen=100));
</pre></li><li class="listitem"><p>
GiST index over <code class="type">ltree[]</code> (<code class="literal">gist__ltree_ops</code>
opclass):
<code class="literal">ltree[] <@ ltree</code>, <code class="literal">ltree @> ltree[]</code>,
<code class="literal">@</code>, <code class="literal">~</code>, <code class="literal">?</code>
</p><p>
<code class="literal">gist__ltree_ops</code> GiST opclass works similarly to
<code class="literal">gist_ltree_ops</code> and also takes signature length as
a parameter. The default value of <code class="literal">siglen</code> in
<code class="literal">gist__ltree_ops</code> is 28 bytes.
</p><p>
Example of creating such an index with the default signature length of 28 bytes:
</p><pre class="programlisting">
CREATE INDEX path_gist_idx ON test USING GIST (array_path);
</pre><p>
Example of creating such an index with a signature length of 100 bytes:
</p><pre class="programlisting">
CREATE INDEX path_gist_idx ON test USING GIST (array_path gist__ltree_ops(siglen=100));
</pre><p>
Note: This index type is lossy.
</p></li></ul></div></div><div class="sect2" id="LTREE-EXAMPLE"><div class="titlepage"><div><div><h3 class="title">F.23.4. Example <a href="#LTREE-EXAMPLE" class="id_link">#</a></h3></div></div></div><p>
This example uses the following data (also available in file
<code class="filename">contrib/ltree/ltreetest.sql</code> in the source distribution):
</p><pre class="programlisting">
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);
</pre><p>
Now, we have a table <code class="structname">test</code> populated with data describing
the hierarchy shown below:
</p><pre class="literallayout">
Top
/ | \
Science Hobbies Collections
/ | \
Astronomy Amateurs_Astronomy Pictures
/ \ |
Astrophysics Cosmology Astronomy
/ | \
Galaxies Stars Astronauts
</pre><p>
We can do inheritance:
</p><pre class="screen">
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)
</pre><p>
</p><p>
Here are some examples of path matching:
</p><pre class="screen">
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)
</pre><p>
</p><p>
Here are some examples of full text search:
</p><pre class="screen">
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)
</pre><p>
</p><p>
Path construction using functions:
</p><pre class="screen">
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)
</pre><p>
</p><p>
We could simplify this by creating an SQL function that inserts a label
at a specified position in a path:
</p><pre class="screen">
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)
</pre><p>
</p></div><div class="sect2" id="LTREE-TRANSFORMS"><div class="titlepage"><div><div><h3 class="title">F.23.5. Transforms <a href="#LTREE-TRANSFORMS" class="id_link">#</a></h3></div></div></div><p>
The <code class="literal">ltree_plpython3u</code> extension implements transforms for
the <code class="type">ltree</code> type for PL/Python. If installed and specified when
creating a function, <code class="type">ltree</code> values are mapped to Python lists.
(The reverse is currently not supported, however.)
</p><div class="caution"><h3 class="title">Caution</h3><p>
It is strongly recommended that the transform extension be installed in
the same schema as <code class="filename">ltree</code>. Otherwise there are
installation-time security hazards if a transform extension's schema
contains objects defined by a hostile user.
</p></div></div><div class="sect2" id="LTREE-AUTHORS"><div class="titlepage"><div><div><h3 class="title">F.23.6. Authors <a href="#LTREE-AUTHORS" class="id_link">#</a></h3></div></div></div><p>
All work was done by Teodor Sigaev (<code class="email"><<a class="email" href="mailto:teodor@stack.net">teodor@stack.net</a>></code>) and
Oleg Bartunov (<code class="email"><<a class="email" href="mailto:oleg@sai.msu.su">oleg@sai.msu.su</a>></code>). See
<a class="ulink" href="http://www.sai.msu.su/~megera/postgres/gist/" target="_top">http://www.sai.msu.su/~megera/postgres/gist/</a> for
additional information. Authors would like to thank Eugeny Rodichev for
helpful discussions. Comments and bug reports are welcome.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="lo.html" title="F.22. lo — manage large objects">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="oldsnapshot.html" title="F.24. old_snapshot — inspect old_snapshot_threshold state">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.22. lo — manage large objects </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> F.24. old_snapshot — inspect <code class="literal">old_snapshot_threshold</code> state</td></tr></table></div></body></html>
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