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   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>52.51. pg_statistic</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="catalog-pg-shseclabel.html" title="52.50. pg_shseclabel" /><link rel="next" href="catalog-pg-statistic-ext.html" title="52.52. pg_statistic_ext" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">52.51. <code class="structname">pg_statistic</code></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="catalog-pg-shseclabel.html" title="52.50. pg_shseclabel">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="catalogs.html" title="Chapter 52. System Catalogs">Up</a></td><th width="60%" align="center">Chapter 52. System Catalogs</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 18.0 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="catalog-pg-statistic-ext.html" title="52.52. pg_statistic_ext">Next</a></td></tr></table><hr /></div><div class="sect1" id="CATALOG-PG-STATISTIC"><div class="titlepage"><div><div><h2 class="title" style="clear: both">52.51. <code class="structname">pg_statistic</code> <a href="#CATALOG-PG-STATISTIC" class="id_link">#</a></h2></div></div></div><a id="id-1.10.4.53.2" class="indexterm"></a><p>
   3    The catalog <code class="structname">pg_statistic</code> stores
   4    statistical data about the contents of the database.  Entries are
   5    created by <a class="link" href="sql-analyze.html" title="ANALYZE"><code class="command">ANALYZE</code></a>
   6    and subsequently used by the query planner.  Note that all the
   7    statistical data is inherently approximate, even assuming that it
   8    is up-to-date.
   9   </p><p>
  10    Normally there is one entry, with <code class="structfield">stainherit</code> =
  11    <code class="literal">false</code>, for each table column that has been analyzed.
  12    If the table has inheritance children or partitions, a second entry with
  13    <code class="structfield">stainherit</code> = <code class="literal">true</code> is also created.  This row
  14    represents the column's statistics over the inheritance tree, i.e.,
  15    statistics for the data you'd see with
  16    <code class="literal">SELECT <em class="replaceable"><code>column</code></em> FROM <em class="replaceable"><code>table</code></em>*</code>,
  17    whereas the <code class="structfield">stainherit</code> = <code class="literal">false</code> row represents
  18    the results of
  19    <code class="literal">SELECT <em class="replaceable"><code>column</code></em> FROM ONLY <em class="replaceable"><code>table</code></em></code>.
  20   </p><p>
  21    <code class="structname">pg_statistic</code> also stores statistical data about
  22    the values of index expressions.  These are described as if they were
  23    actual data columns; in particular, <code class="structfield">starelid</code>
  24    references the index.  No entry is made for an ordinary non-expression
  25    index column, however, since it would be redundant with the entry
  26    for the underlying table column.  Currently, entries for index expressions
  27    always have <code class="structfield">stainherit</code> = <code class="literal">false</code>.
  28   </p><p>
  29    Since different kinds of statistics might be appropriate for different
  30    kinds of data, <code class="structname">pg_statistic</code> is designed not
  31    to assume very much about what sort of statistics it stores.  Only
  32    extremely general statistics (such as nullness) are given dedicated
  33    columns in <code class="structname">pg_statistic</code>.  Everything else
  34    is stored in <span class="quote">“<span class="quote">slots</span>”</span>, which are groups of associated columns
  35    whose content is identified by a code number in one of the slot's columns.
  36    For more information see
  37    <code class="filename">src/include/catalog/pg_statistic.h</code>.
  38   </p><p>
  39    <code class="structname">pg_statistic</code> should not be readable by the
  40    public, since even statistical information about a table's contents
  41    might be considered sensitive.  (Example: minimum and maximum values
  42    of a salary column might be quite interesting.)
  43    <a class="link" href="view-pg-stats.html" title="53.29. pg_stats"><code class="structname">pg_stats</code></a>
  44    is a publicly readable view on
  45    <code class="structname">pg_statistic</code> that only exposes information
  46    about those tables that are readable by the current user.
  47   </p><div class="table" id="id-1.10.4.53.8"><p class="title"><strong>Table 52.51. <code class="structname">pg_statistic</code> Columns</strong></p><div class="table-contents"><table class="table" summary="pg_statistic Columns" border="1"><colgroup><col /></colgroup><thead><tr><th class="catalog_table_entry"><p class="column_definition">
  48        Column Type
  49       </p>
  50       <p>
  51        Description
  52       </p></th></tr></thead><tbody><tr><td class="catalog_table_entry"><p class="column_definition">
  53        <code class="structfield">starelid</code> <code class="type">oid</code>
  54        (references <a class="link" href="catalog-pg-class.html" title="52.11. pg_class"><code class="structname">pg_class</code></a>.<code class="structfield">oid</code>)
  55       </p>
  56       <p>
  57        The table or index that the described column belongs to
  58       </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
  59        <code class="structfield">staattnum</code> <code class="type">int2</code>
  60        (references <a class="link" href="catalog-pg-attribute.html" title="52.7. pg_attribute"><code class="structname">pg_attribute</code></a>.<code class="structfield">attnum</code>)
  61       </p>
  62       <p>
  63        The number of the described column
  64       </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
  65        <code class="structfield">stainherit</code> <code class="type">bool</code>
  66       </p>
  67       <p>
  68        If true, the stats include values from child tables, not just the
  69        values in the specified relation
  70       </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
  71        <code class="structfield">stanullfrac</code> <code class="type">float4</code>
  72       </p>
  73       <p>
  74        The fraction of the column's entries that are null
  75       </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
  76        <code class="structfield">stawidth</code> <code class="type">int4</code>
  77       </p>
  78       <p>
  79        The average stored width, in bytes, of nonnull entries
  80       </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
  81        <code class="structfield">stadistinct</code> <code class="type">float4</code>
  82       </p>
  83       <p>
  84        The number of distinct nonnull data values in the column.
  85        A value greater than zero is the actual number of distinct values.
  86        A value less than zero is the negative of a multiplier for the number
  87        of rows in the table; for example, a column in which about 80% of the
  88        values are nonnull and each nonnull value appears about twice on
  89        average could be represented by <code class="structfield">stadistinct</code> = -0.4.
  90        A zero value means the number of distinct values is unknown.
  91       </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
  92        <code class="structfield">stakind<em class="replaceable"><code>N</code></em></code> <code class="type">int2</code>
  93       </p>
  94       <p>
  95        A code number indicating the kind of statistics stored in the
  96        <em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span> of the
  97        <code class="structname">pg_statistic</code> row.
  98       </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
  99        <code class="structfield">staop<em class="replaceable"><code>N</code></em></code> <code class="type">oid</code>
 100        (references <a class="link" href="catalog-pg-operator.html" title="52.34. pg_operator"><code class="structname">pg_operator</code></a>.<code class="structfield">oid</code>)
 101       </p>
 102       <p>
 103        An operator used to derive the statistics stored in the
 104        <em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span>.  For example, a
 105        histogram slot would show the <code class="literal">&lt;</code> operator
 106        that defines the sort order of the data.
 107        Zero if the statistics kind does not require an operator.
 108       </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
 109        <code class="structfield">stacoll<em class="replaceable"><code>N</code></em></code> <code class="type">oid</code>
 110        (references <a class="link" href="catalog-pg-collation.html" title="52.12. pg_collation"><code class="structname">pg_collation</code></a>.<code class="structfield">oid</code>)
 111       </p>
 112       <p>
 113        The collation used to derive the statistics stored in the
 114        <em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span>.  For example, a
 115        histogram slot for a collatable column would show the collation that
 116        defines the sort order of the data.  Zero for noncollatable data.
 117       </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
 118        <code class="structfield">stanumbers<em class="replaceable"><code>N</code></em></code> <code class="type">float4[]</code>
 119       </p>
 120       <p>
 121        Numerical statistics of the appropriate kind for the
 122        <em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span>, or null if the slot
 123        kind does not involve numerical values
 124       </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
 125        <code class="structfield">stavalues<em class="replaceable"><code>N</code></em></code> <code class="type">anyarray</code>
 126       </p>
 127       <p>
 128        Column data values of the appropriate kind for the
 129        <em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span>, or null if the slot
 130        kind does not store any data values.  Each array's element
 131        values are actually of the specific column's data type, or a related
 132        type such as an array's element type, so there is no way to define
 133        these columns' type more specifically than <code class="type">anyarray</code>.
 134       </p></td></tr></tbody></table></div></div><br class="table-break" /></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="catalog-pg-shseclabel.html" title="52.50. pg_shseclabel">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="catalogs.html" title="Chapter 52. System Catalogs">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="catalog-pg-statistic-ext.html" title="52.52. pg_statistic_ext">Next</a></td></tr><tr><td width="40%" align="left" valign="top">52.50. <code class="structname">pg_shseclabel</code> </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 18.0 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 52.52. <code class="structname">pg_statistic_ext</code></td></tr></table></div></body></html>