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Green_GoodERP18_FSJ_Standard/PostgreSQL/doc/postgresql/html/btree-support-funcs.html

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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!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 V1.79.1" /><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 12.4 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>

  3.   As shown in <a class="xref" href="xindex.html#XINDEX-BTREE-SUPPORT-TABLE" title="Table 37.8. B-Tree Support Functions">Table 37.8</a>, btree defines

  4.   one required and two optional support functions.

  5.  </p><p>

  6.   For each combination of data types that a btree operator family provides

  7.   comparison operators for, it must provide a comparison support function,

  8.   registered in <code class="structname">pg_amproc</code> with support function

  9.   number 1 and

  10.   <code class="structfield">amproclefttype</code>/<code class="structfield">amprocrighttype</code>

  11.   equal to the left and right data types for the comparison (i.e., the

  12.   same data types that the matching operators are registered with

  13.   in <code class="structname">pg_amop</code>).

  14.   The comparison function must take two non-null values

  15.   <em class="replaceable"><code>A</code></em> and <em class="replaceable"><code>B</code></em> and

  16.   return an <code class="type">int32</code> value that

  17.   is <code class="literal">&lt;</code> <code class="literal">0</code>, <code class="literal">0</code>,

  18.   or <code class="literal">&gt;</code> <code class="literal">0</code>

  19.   when <em class="replaceable"><code>A</code></em> <code class="literal">&lt;</code>

  20.   <em class="replaceable"><code>B</code></em>, <em class="replaceable"><code>A</code></em>

  21.   <code class="literal">=</code> <em class="replaceable"><code>B</code></em>,

  22.   or <em class="replaceable"><code>A</code></em> <code class="literal">&gt;</code>

  23.   <em class="replaceable"><code>B</code></em>, respectively.

  24.   A null result is disallowed: all values of the data type must be comparable.

  25.   See <code class="filename">src/backend/access/nbtree/nbtcompare.c</code> for

  26.   examples.

  27.  </p><p>

  28.   If the compared values are of a collatable data type, the appropriate

  29.   collation OID will be passed to the comparison support function, using

  30.   the standard <code class="function">PG_GET_COLLATION()</code> mechanism.

  31.  </p><p>

  32.   Optionally, a btree operator family may provide <em class="firstterm">sort

  33.   support</em> function(s), registered under support function number

  34.   2.  These functions allow implementing comparisons for sorting purposes

  35.   in a more efficient way than naively calling the comparison support

  36.   function.  The APIs involved in this are defined in

  37.   <code class="filename">src/include/utils/sortsupport.h</code>.

  38.  </p><a id="id-1.10.16.5.6" class="indexterm"></a><a id="id-1.10.16.5.7" class="indexterm"></a><p>

  39.   Optionally, a btree operator family may

  40.   provide <em class="firstterm">in_range</em> support function(s), registered

  41.   under support function number 3.  These are not used during btree index

  42.   operations; rather, they extend the semantics of the operator family so

  43.   that it can support window clauses containing

  44.   the <code class="literal">RANGE</code> <em class="replaceable"><code>offset</code></em>

  45.   <code class="literal">PRECEDING</code>

  46.   and <code class="literal">RANGE</code> <em class="replaceable"><code>offset</code></em>

  47.   <code class="literal">FOLLOWING</code> frame bound types (see

  48.   <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

  49.   information provided is how to add or subtract

  50.   an <em class="replaceable"><code>offset</code></em> value in a way that is compatible

  51.   with the family's data ordering.

  52.  </p><p>

  53.   An <code class="function">in_range</code> function must have the signature

  54. </p><pre class="synopsis">

  55. 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)

  56. returns bool

  57. </pre><p>

  58.   <em class="replaceable"><code>val</code></em> and <em class="replaceable"><code>base</code></em> must be

  59.   of the same type, which is one of the types supported by the operator

  60.   family (i.e., a type for which it provides an ordering).

  61.   However, <em class="replaceable"><code>offset</code></em> could be of a different type,

  62.   which might be one otherwise unsupported by the family.  An example is

  63.   that the built-in <code class="literal">time_ops</code> family provides

  64.   an <code class="function">in_range</code> function that

  65.   has <em class="replaceable"><code>offset</code></em> of type <code class="type">interval</code>.

  66.   A family can provide <code class="function">in_range</code> functions for any of

  67.   its supported types and one or more <em class="replaceable"><code>offset</code></em>

  68.   types.  Each <code class="function">in_range</code> function should be entered

  69.   in <code class="structname">pg_amproc</code>

  70.   with <code class="structfield">amproclefttype</code> equal to <code class="type">type1</code>

  71.   and <code class="structfield">amprocrighttype</code> equal to <code class="type">type2</code>.

  72.  </p><p>

  73.   The essential semantics of an <code class="function">in_range</code> function

  74.   depend on the two Boolean flag parameters.  It should add or

  75.   subtract <em class="replaceable"><code>base</code></em>

  76.   and <em class="replaceable"><code>offset</code></em>, then

  77.   compare <em class="replaceable"><code>val</code></em> to the result, as follows:

  78.   </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  79.      if <code class="literal">!</code><em class="replaceable"><code>sub</code></em> and

  80.      <code class="literal">!</code><em class="replaceable"><code>less</code></em>,

  81.      return <em class="replaceable"><code>val</code></em> <code class="literal">&gt;=</code>

  82.      (<em class="replaceable"><code>base</code></em> <code class="literal">+</code>

  83.      <em class="replaceable"><code>offset</code></em>)

  84.     </p></li><li class="listitem"><p>

  85.      if <code class="literal">!</code><em class="replaceable"><code>sub</code></em>

  86.      and <em class="replaceable"><code>less</code></em>,

  87.      return <em class="replaceable"><code>val</code></em> <code class="literal">&lt;=</code>

  88.      (<em class="replaceable"><code>base</code></em> <code class="literal">+</code>

  89.      <em class="replaceable"><code>offset</code></em>)

  90.     </p></li><li class="listitem"><p>

  91.      if <em class="replaceable"><code>sub</code></em>

  92.      and <code class="literal">!</code><em class="replaceable"><code>less</code></em>,

  93.      return <em class="replaceable"><code>val</code></em> <code class="literal">&gt;=</code>

  94.      (<em class="replaceable"><code>base</code></em> <code class="literal">-</code>

  95.      <em class="replaceable"><code>offset</code></em>)

  96.     </p></li><li class="listitem"><p>

  97.      if <em class="replaceable"><code>sub</code></em> and <em class="replaceable"><code>less</code></em>,

  98.      return <em class="replaceable"><code>val</code></em> <code class="literal">&lt;=</code>

  99.      (<em class="replaceable"><code>base</code></em> <code class="literal">-</code>

  100.      <em class="replaceable"><code>offset</code></em>)

  101.     </p></li></ul></div><p>

  102.   Before doing so, the function should check the sign

  103.   of <em class="replaceable"><code>offset</code></em>: if it is less than zero, raise

  104.   error <code class="literal">ERRCODE_INVALID_PRECEDING_OR_FOLLOWING_SIZE</code> (22013)

  105.   with error text like <span class="quote">“<span class="quote">invalid preceding or following size in window

  106.   function</span>”</span>.  (This is required by the SQL standard, although

  107.   nonstandard operator families might perhaps choose to ignore this

  108.   restriction, since there seems to be little semantic necessity for it.)

  109.   This requirement is delegated to the <code class="function">in_range</code>

  110.   function so that the core code needn't understand what <span class="quote">“<span class="quote">less than

  111.   zero</span>”</span> means for a particular data type.

  112.  </p><p>

  113.   An additional expectation is that <code class="function">in_range</code> functions

  114.   should, if practical, avoid throwing an error

  115.   if <em class="replaceable"><code>base</code></em> <code class="literal">+</code>

  116.   <em class="replaceable"><code>offset</code></em>

  117.   or <em class="replaceable"><code>base</code></em> <code class="literal">-</code>

  118.   <em class="replaceable"><code>offset</code></em> would overflow.

  119.   The correct comparison result can be determined even if that value would

  120.   be out of the data type's range.  Note that if the data type includes

  121.   concepts such as <span class="quote">“<span class="quote">infinity</span>”</span> or <span class="quote">“<span class="quote">NaN</span>”</span>, extra care

  122.   may be needed to ensure that <code class="function">in_range</code>'s results agree

  123.   with the normal sort order of the operator family.

  124.  </p><p>

  125.   The results of the <code class="function">in_range</code> function must be

  126.   consistent with the sort ordering imposed by the operator family.

  127.   To be precise, given any fixed values of <em class="replaceable"><code>offset</code></em>

  128.   and <em class="replaceable"><code>sub</code></em>, then:

  129.   </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  130.      If <code class="function">in_range</code> with <em class="replaceable"><code>less</code></em> =

  131.      true is true for some <em class="replaceable"><code>val1</code></em>

  132.      and <em class="replaceable"><code>base</code></em>, it must be true for

  133.      every <em class="replaceable"><code>val2</code></em> <code class="literal">&lt;=</code>

  134.      <em class="replaceable"><code>val1</code></em> with the

  135.      same <em class="replaceable"><code>base</code></em>.

  136.     </p></li><li class="listitem"><p>

  137.      If <code class="function">in_range</code> with <em class="replaceable"><code>less</code></em> =

  138.      true is false for some <em class="replaceable"><code>val1</code></em>

  139.      and <em class="replaceable"><code>base</code></em>, it must be false for

  140.      every <em class="replaceable"><code>val2</code></em> <code class="literal">&gt;=</code>

  141.      <em class="replaceable"><code>val1</code></em> with the

  142.      same <em class="replaceable"><code>base</code></em>.

  143.     </p></li><li class="listitem"><p>

  144.      If <code class="function">in_range</code> with <em class="replaceable"><code>less</code></em> =

  145.      true is true for some <em class="replaceable"><code>val</code></em>

  146.      and <em class="replaceable"><code>base1</code></em>, it must be true for

  147.      every <em class="replaceable"><code>base2</code></em> <code class="literal">&gt;=</code>

  148.      <em class="replaceable"><code>base1</code></em> with the

  149.      same <em class="replaceable"><code>val</code></em>.

  150.     </p></li><li class="listitem"><p>

  151.      If <code class="function">in_range</code> with <em class="replaceable"><code>less</code></em> =

  152.      true is false for some <em class="replaceable"><code>val</code></em>

  153.      and <em class="replaceable"><code>base1</code></em>, it must be false for

  154.      every <em class="replaceable"><code>base2</code></em> <code class="literal">&lt;=</code>

  155.      <em class="replaceable"><code>base1</code></em> with the

  156.      same <em class="replaceable"><code>val</code></em>.

  157.     </p></li></ul></div><p>

  158.   Analogous statements with inverted conditions hold

  159.   when <em class="replaceable"><code>less</code></em> = false.

  160.  </p><p>

  161.   If the type being ordered (<code class="type">type1</code>) is collatable,

  162.   the appropriate collation OID will be passed to

  163.   the <code class="function">in_range</code> function, using the standard

  164.   PG_GET_COLLATION() mechanism.

  165.  </p><p>

  166.   <code class="function">in_range</code> functions need not handle NULL inputs, and

  167.   typically will be marked strict.

  168.  </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>
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