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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>52.50. 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="52.49. pg_shseclabel" /><link rel="next" href="catalog-pg-statistic-ext.html" title="52.51. pg_statistic_ext" /></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">52.50. <code xmlns="http://www.w3.org/1999/xhtml" class="structname">pg_statistic</code></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="catalog-pg-shseclabel.html" title="52.49. 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 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="catalog-pg-statistic-ext.html" title="52.51. pg_statistic_ext">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="CATALOG-PG-STATISTIC"><div class="titlepage"><div><div><h2 class="title" style="clear: both">52.50. <code class="structname">pg_statistic</code></h2></div></div></div><a id="id-1.10.4.52.2" class="indexterm"></a><p>
The catalog <code class="structname">pg_statistic</code> stores
statistical data about the contents of the database. Entries are
created by <a class="xref" href="sql-analyze.html" title="ANALYZE"><span class="refentrytitle">ANALYZE</span></a>
and subsequently used by the query planner. Note that all the
statistical data is inherently approximate, even assuming that it
is up-to-date.
</p><p>
Normally there is one entry, with <code class="structfield">stainherit</code> =
<code class="literal">false</code>, for each table column that has been analyzed.
If the table has inheritance children, a second entry with
<code class="structfield">stainherit</code> = <code class="literal">true</code> is also created. This row
represents the column's statistics over the inheritance tree, i.e.,
statistics for the data you'd see with
<code class="literal">SELECT <em class="replaceable"><code>column</code></em> FROM <em class="replaceable"><code>table</code></em>*</code>,
whereas the <code class="structfield">stainherit</code> = <code class="literal">false</code> row represents
the results of
<code class="literal">SELECT <em class="replaceable"><code>column</code></em> FROM ONLY <em class="replaceable"><code>table</code></em></code>.
</p><p>
<code class="structname">pg_statistic</code> also stores statistical data about
the values of index expressions. These are described as if they were
actual data columns; in particular, <code class="structfield">starelid</code>
references the index. No entry is made for an ordinary non-expression
index column, however, since it would be redundant with the entry
for the underlying table column. Currently, entries for index expressions
always have <code class="structfield">stainherit</code> = <code class="literal">false</code>.
</p><p>
Since different kinds of statistics might be appropriate for different
kinds of data, <code class="structname">pg_statistic</code> is designed not
to assume very much about what sort of statistics it stores. Only
extremely general statistics (such as nullness) are given dedicated
columns in <code class="structname">pg_statistic</code>. Everything else
is stored in <span class="quote">“<span class="quote">slots</span>”</span>, which are groups of associated columns
whose content is identified by a code number in one of the slot's columns.
For more information see
<code class="filename">src/include/catalog/pg_statistic.h</code>.
</p><p>
<code class="structname">pg_statistic</code> should not be readable by the
public, since even statistical information about a table's contents
might be considered sensitive. (Example: minimum and maximum values
of a salary column might be quite interesting.)
<a class="link" href="view-pg-stats.html" title="52.87. pg_stats"><code class="structname">pg_stats</code></a>
is a publicly readable view on
<code class="structname">pg_statistic</code> that only exposes information
about those tables that are readable by the current user.
</p><div class="table" id="id-1.10.4.52.8"><p class="title"><strong>Table 52.50. <code class="structname">pg_statistic</code> Columns</strong></p><div class="table-contents"><table class="table" summary="pg_statistic Columns" border="1"><colgroup><col /><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Type</th><th>References</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">starelid</code></td><td><code class="type">oid</code></td><td><code class="literal"><a class="link" href="catalog-pg-class.html" title="52.11. pg_class"><code class="structname">pg_class</code></a>.oid</code></td><td>The table or index that the described column belongs to</td></tr><tr><td><code class="structfield">staattnum</code></td><td><code class="type">int2</code></td><td><code class="literal"><a class="link" href="catalog-pg-attribute.html" title="52.7. pg_attribute"><code class="structname">pg_attribute</code></a>.attnum</code></td><td>The number of the described column</td></tr><tr><td><code class="structfield">stainherit</code></td><td><code class="type">bool</code></td><td> </td><td>If true, the stats include inheritance child columns, not just the
values in the specified relation</td></tr><tr><td><code class="structfield">stanullfrac</code></td><td><code class="type">float4</code></td><td> </td><td>The fraction of the column's entries that are null</td></tr><tr><td><code class="structfield">stawidth</code></td><td><code class="type">int4</code></td><td> </td><td>The average stored width, in bytes, of nonnull entries</td></tr><tr><td><code class="structfield">stadistinct</code></td><td><code class="type">float4</code></td><td> </td><td>The number of distinct nonnull data values in the column.
A value greater than zero is the actual number of distinct values.
A value less than zero is the negative of a multiplier for the number
of rows in the table; for example, a column in which about 80% of the
values are nonnull and each nonnull value appears about twice on
average could be represented by <code class="structfield">stadistinct</code> = -0.4.
A zero value means the number of distinct values is unknown.
</td></tr><tr><td><code class="structfield">stakind<em class="replaceable"><code>N</code></em></code></td><td><code class="type">int2</code></td><td> </td><td>
A code number indicating the kind of statistics stored in the
<em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span> of the
<code class="structname">pg_statistic</code> row.
</td></tr><tr><td><code class="structfield">staop<em class="replaceable"><code>N</code></em></code></td><td><code class="type">oid</code></td><td><code class="literal"><a class="link" href="catalog-pg-operator.html" title="52.34. pg_operator"><code class="structname">pg_operator</code></a>.oid</code></td><td>
An operator used to derive the statistics stored in the
<em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span>. For example, a
histogram slot would show the <code class="literal"><</code> operator
that defines the sort order of the data.
</td></tr><tr><td><code class="structfield">stanumbers<em class="replaceable"><code>N</code></em></code></td><td><code class="type">float4[]</code></td><td> </td><td>
Numerical statistics of the appropriate kind for the
<em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span>, or null if the slot
kind does not involve numerical values
</td></tr><tr><td><code class="structfield">stavalues<em class="replaceable"><code>N</code></em></code></td><td><code class="type">anyarray</code></td><td> </td><td>
Column data values of the appropriate kind for the
<em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span>, or null if the slot
kind does not store any data values. Each array's element
values are actually of the specific column's data type, or a related
type such as an array's element type, so there is no way to define
these columns' type more specifically than <code class="type">anyarray</code>.
</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">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="catalogs.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="catalog-pg-statistic-ext.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">52.49. <code class="structname">pg_shseclabel</code> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 52.51. <code class="structname">pg_statistic_ext</code></td></tr></table></div></body></html>
