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<!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>63.3. B-Tree Support Functions</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="btree-behavior.html" title="63.2. Behavior of B-Tree Operator Classes" /><link rel="next" href="btree-implementation.html" title="63.4. Implementation" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">63.3. B-Tree Support Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="btree-behavior.html" title="63.2. Behavior of B-Tree Operator Classes">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="btree.html" title="Chapter 63. B-Tree Indexes">Up</a></td><th width="60%" align="center">Chapter 63. B-Tree Indexes</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="btree-implementation.html" title="63.4. Implementation">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="BTREE-SUPPORT-FUNCS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">63.3. B-Tree Support Functions</h2></div></div></div><p>
As shown in <a class="xref" href="xindex.html#XINDEX-BTREE-SUPPORT-TABLE" title="Table 38.8. B-tree Support Functions">Table 38.8</a>, btree defines
one required and two optional support functions.
</p><p>
For each combination of data types that a btree operator family provides
comparison operators for, it must provide a comparison support function,
registered in <code class="structname">pg_amproc</code> with support function
number 1 and
<code class="structfield">amproclefttype</code>/<code class="structfield">amprocrighttype</code>
equal to the left and right data types for the comparison (i.e., the
same data types that the matching operators are registered with
in <code class="structname">pg_amop</code>).
The comparison function must take two non-null values
<em class="replaceable"><code>A</code></em> and <em class="replaceable"><code>B</code></em> and
return an <code class="type">int32</code> value that
is <code class="literal"><</code> <code class="literal">0</code>, <code class="literal">0</code>,
or <code class="literal">></code> <code class="literal">0</code>
when <em class="replaceable"><code>A</code></em> <code class="literal"><</code>
<em class="replaceable"><code>B</code></em>, <em class="replaceable"><code>A</code></em>
<code class="literal">=</code> <em class="replaceable"><code>B</code></em>,
or <em class="replaceable"><code>A</code></em> <code class="literal">></code>
<em class="replaceable"><code>B</code></em>, respectively.
A null result is disallowed: all values of the data type must be comparable.
See <code class="filename">src/backend/access/nbtree/nbtcompare.c</code> for
examples.
</p><p>
If the compared values are of a collatable data type, the appropriate
collation OID will be passed to the comparison support function, using
the standard <code class="function">PG_GET_COLLATION()</code> mechanism.
</p><p>
Optionally, a btree operator family may provide <em class="firstterm">sort
support</em> function(s), registered under support function number
2. These functions allow implementing comparisons for sorting purposes
in a more efficient way than naively calling the comparison support
function. The APIs involved in this are defined in
<code class="filename">src/include/utils/sortsupport.h</code>.
</p><a id="id-1.10.15.5.6" class="indexterm"></a><a id="id-1.10.15.5.7" class="indexterm"></a><p>
Optionally, a btree operator family may
provide <em class="firstterm">in_range</em> support function(s), registered
under support function number 3. These are not used during btree index
operations; rather, they extend the semantics of the operator family so
that it can support window clauses containing
the <code class="literal">RANGE</code> <em class="replaceable"><code>offset</code></em>
<code class="literal">PRECEDING</code>
and <code class="literal">RANGE</code> <em class="replaceable"><code>offset</code></em>
<code class="literal">FOLLOWING</code> frame bound types (see
<a class="xref" href="sql-expressions.html#SYNTAX-WINDOW-FUNCTIONS" title="4.2.8. Window Function Calls">Section 4.2.8</a>). Fundamentally, the extra
information provided is how to add or subtract
an <em class="replaceable"><code>offset</code></em> value in a way that is compatible
with the family's data ordering.
</p><p>
An <code class="function">in_range</code> function must have the signature
</p><pre class="synopsis">
in_range(<em class="replaceable"><code>val</code></em> type1, <em class="replaceable"><code>base</code></em> type1, <em class="replaceable"><code>offset</code></em> type2, <em class="replaceable"><code>sub</code></em> bool, <em class="replaceable"><code>less</code></em> bool)
returns bool
</pre><p>
<em class="replaceable"><code>val</code></em> and <em class="replaceable"><code>base</code></em> must be
of the same type, which is one of the types supported by the operator
family (i.e., a type for which it provides an ordering).
However, <em class="replaceable"><code>offset</code></em> could be of a different type,
which might be one otherwise unsupported by the family. An example is
that the built-in <code class="literal">time_ops</code> family provides
an <code class="function">in_range</code> function that
has <em class="replaceable"><code>offset</code></em> of type <code class="type">interval</code>.
A family can provide <code class="function">in_range</code> functions for any of
its supported types and one or more <em class="replaceable"><code>offset</code></em>
types. Each <code class="function">in_range</code> function should be entered
in <code class="structname">pg_amproc</code>
with <code class="structfield">amproclefttype</code> equal to <code class="type">type1</code>
and <code class="structfield">amprocrighttype</code> equal to <code class="type">type2</code>.
</p><p>
The essential semantics of an <code class="function">in_range</code> function
depend on the two boolean flag parameters. It should add or
subtract <em class="replaceable"><code>base</code></em>
and <em class="replaceable"><code>offset</code></em>, then
compare <em class="replaceable"><code>val</code></em> to the result, as follows:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
if <code class="literal">!</code><em class="replaceable"><code>sub</code></em> and
<code class="literal">!</code><em class="replaceable"><code>less</code></em>,
return <em class="replaceable"><code>val</code></em> <code class="literal">>=</code>
(<em class="replaceable"><code>base</code></em> <code class="literal">+</code>
<em class="replaceable"><code>offset</code></em>)
</p></li><li class="listitem"><p>
if <code class="literal">!</code><em class="replaceable"><code>sub</code></em>
and <em class="replaceable"><code>less</code></em>,
return <em class="replaceable"><code>val</code></em> <code class="literal"><=</code>
(<em class="replaceable"><code>base</code></em> <code class="literal">+</code>
<em class="replaceable"><code>offset</code></em>)
</p></li><li class="listitem"><p>
if <em class="replaceable"><code>sub</code></em>
and <code class="literal">!</code><em class="replaceable"><code>less</code></em>,
return <em class="replaceable"><code>val</code></em> <code class="literal">>=</code>
(<em class="replaceable"><code>base</code></em> <code class="literal">-</code>
<em class="replaceable"><code>offset</code></em>)
</p></li><li class="listitem"><p>
if <em class="replaceable"><code>sub</code></em> and <em class="replaceable"><code>less</code></em>,
return <em class="replaceable"><code>val</code></em> <code class="literal"><=</code>
(<em class="replaceable"><code>base</code></em> <code class="literal">-</code>
<em class="replaceable"><code>offset</code></em>)
</p></li></ul></div><p>
Before doing so, the function should check the sign
of <em class="replaceable"><code>offset</code></em>: if it is less than zero, raise
error <code class="literal">ERRCODE_INVALID_PRECEDING_OR_FOLLOWING_SIZE</code> (22013)
with error text like <span class="quote">“<span class="quote">invalid preceding or following size in window
function</span>”</span>. (This is required by the SQL standard, although
nonstandard operator families might perhaps choose to ignore this
restriction, since there seems to be little semantic necessity for it.)
This requirement is delegated to the <code class="function">in_range</code>
function so that the core code needn't understand what <span class="quote">“<span class="quote">less than
zero</span>”</span> means for a particular data type.
</p><p>
An additional expectation is that <code class="function">in_range</code> functions
should, if practical, avoid throwing an error
if <em class="replaceable"><code>base</code></em> <code class="literal">+</code>
<em class="replaceable"><code>offset</code></em>
or <em class="replaceable"><code>base</code></em> <code class="literal">-</code>
<em class="replaceable"><code>offset</code></em> would overflow.
The correct comparison result can be determined even if that value would
be out of the data type's range. Note that if the data type includes
concepts such as <span class="quote">“<span class="quote">infinity</span>”</span> or <span class="quote">“<span class="quote">NaN</span>”</span>, extra care
may be needed to ensure that <code class="function">in_range</code>'s results agree
with the normal sort order of the operator family.
</p><p>
The results of the <code class="function">in_range</code> function must be
consistent with the sort ordering imposed by the operator family.
To be precise, given any fixed values of <em class="replaceable"><code>offset</code></em>
and <em class="replaceable"><code>sub</code></em>, then:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
If <code class="function">in_range</code> with <em class="replaceable"><code>less</code></em> =
true is true for some <em class="replaceable"><code>val1</code></em>
and <em class="replaceable"><code>base</code></em>, it must be true for
every <em class="replaceable"><code>val2</code></em> <code class="literal"><=</code>
<em class="replaceable"><code>val1</code></em> with the
same <em class="replaceable"><code>base</code></em>.
</p></li><li class="listitem"><p>
If <code class="function">in_range</code> with <em class="replaceable"><code>less</code></em> =
true is false for some <em class="replaceable"><code>val1</code></em>
and <em class="replaceable"><code>base</code></em>, it must be false for
every <em class="replaceable"><code>val2</code></em> <code class="literal">>=</code>
<em class="replaceable"><code>val1</code></em> with the
same <em class="replaceable"><code>base</code></em>.
</p></li><li class="listitem"><p>
If <code class="function">in_range</code> with <em class="replaceable"><code>less</code></em> =
true is true for some <em class="replaceable"><code>val</code></em>
and <em class="replaceable"><code>base1</code></em>, it must be true for
every <em class="replaceable"><code>base2</code></em> <code class="literal">>=</code>
<em class="replaceable"><code>base1</code></em> with the
same <em class="replaceable"><code>val</code></em>.
</p></li><li class="listitem"><p>
If <code class="function">in_range</code> with <em class="replaceable"><code>less</code></em> =
true is false for some <em class="replaceable"><code>val</code></em>
and <em class="replaceable"><code>base1</code></em>, it must be false for
every <em class="replaceable"><code>base2</code></em> <code class="literal"><=</code>
<em class="replaceable"><code>base1</code></em> with the
same <em class="replaceable"><code>val</code></em>.
</p></li></ul></div><p>
Analogous statements with inverted conditions hold
when <em class="replaceable"><code>less</code></em> = false.
</p><p>
If the type being ordered (<code class="type">type1</code>) is collatable,
the appropriate collation OID will be passed to
the <code class="function">in_range</code> function, using the standard
PG_GET_COLLATION() mechanism.
</p><p>
<code class="function">in_range</code> functions need not handle NULL inputs, and
typically will be marked strict.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="btree-behavior.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="btree.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="btree-implementation.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">63.2. Behavior of B-Tree Operator Classes </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 63.4. Implementation</td></tr></table></div></body></html>
