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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>52.91. pg_stats_ext_exprs</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="view-pg-stats-ext.html" title="52.90. pg_stats_ext" /><link rel="next" href="view-pg-tables.html" title="52.92. pg_tables" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">52.91. <code xmlns="http://www.w3.org/1999/xhtml" class="structname">pg_stats_ext_exprs</code></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="view-pg-stats-ext.html" title="52.90. pg_stats_ext">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 14.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="view-pg-tables.html" title="52.92. pg_tables">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="VIEW-PG-STATS-EXT-EXPRS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">52.91. <code class="structname">pg_stats_ext_exprs</code></h2></div></div></div><a id="id-1.10.4.93.2" class="indexterm"></a><p>
The view <code class="structname">pg_stats_ext_exprs</code> provides access to
information about all expressions included in extended statistics objects,
combining information stored in the <a class="link" href="catalog-pg-statistic-ext.html" title="52.50. pg_statistic_ext"><code class="structname">pg_statistic_ext</code></a>
and <a class="link" href="catalog-pg-statistic-ext-data.html" title="52.51. pg_statistic_ext_data"><code class="structname">pg_statistic_ext_data</code></a>
catalogs. This view allows access only to rows of
<a class="link" href="catalog-pg-statistic-ext.html" title="52.50. pg_statistic_ext"><code class="structname">pg_statistic_ext</code></a> and <a class="link" href="catalog-pg-statistic-ext-data.html" title="52.51. pg_statistic_ext_data"><code class="structname">pg_statistic_ext_data</code></a>
that correspond to tables the user has permission to read, and therefore
it is safe to allow public read access to this view.
</p><p>
<code class="structname">pg_stats_ext_exprs</code> is also designed to present
the information in a more readable format than the underlying catalogs
— at the cost that its schema must be extended whenever the structure
of statistics in <code class="structname">pg_statistic_ext</code> changes.
</p><div class="table" id="id-1.10.4.93.5"><p class="title"><strong>Table 52.92. <code class="structname">pg_stats_ext_exprs</code> Columns</strong></p><div class="table-contents"><table class="table" summary="pg_stats_ext_exprs Columns" border="1"><colgroup><col /></colgroup><thead><tr><th class="catalog_table_entry"><p class="column_definition">
Column Type
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">schemaname</code> <code class="type">name</code>
(references <a class="link" href="catalog-pg-namespace.html" title="52.32. pg_namespace"><code class="structname">pg_namespace</code></a>.<code class="structfield">nspname</code>)
</p>
<p>
Name of schema containing table
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">tablename</code> <code class="type">name</code>
(references <a class="link" href="catalog-pg-class.html" title="52.11. pg_class"><code class="structname">pg_class</code></a>.<code class="structfield">relname</code>)
</p>
<p>
Name of table the statistics object is defined on
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">statistics_schemaname</code> <code class="type">name</code>
(references <a class="link" href="catalog-pg-namespace.html" title="52.32. pg_namespace"><code class="structname">pg_namespace</code></a>.<code class="structfield">nspname</code>)
</p>
<p>
Name of schema containing extended statistics object
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">statistics_name</code> <code class="type">name</code>
(references <a class="link" href="catalog-pg-statistic-ext.html" title="52.50. pg_statistic_ext"><code class="structname">pg_statistic_ext</code></a>.<code class="structfield">stxname</code>)
</p>
<p>
Name of extended statistics object
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">statistics_owner</code> <code class="type">name</code>
(references <a class="link" href="catalog-pg-authid.html" title="52.8. pg_authid"><code class="structname">pg_authid</code></a>.<code class="structfield">rolname</code>)
</p>
<p>
Owner of the extended statistics object
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">expr</code> <code class="type">text</code>
</p>
<p>
Expression included in the extended statistics object
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">null_frac</code> <code class="type">float4</code>
</p>
<p>
Fraction of expression entries that are null
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">avg_width</code> <code class="type">int4</code>
</p>
<p>
Average width in bytes of expression's entries
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">n_distinct</code> <code class="type">float4</code>
</p>
<p>
If greater than zero, the estimated number of distinct values in the
expression. If less than zero, the negative of the number of distinct
values divided by the number of rows. (The negated form is used when
<code class="command">ANALYZE</code> believes that the number of distinct values is
likely to increase as the table grows; the positive form is used when
the expression seems to have a fixed number of possible values.) For
example, -1 indicates a unique expression in which the number of distinct
values is the same as the number of rows.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">most_common_vals</code> <code class="type">anyarray</code>
</p>
<p>
A list of the most common values in the expression. (Null if
no values seem to be more common than any others.)
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">most_common_freqs</code> <code class="type">float4[]</code>
</p>
<p>
A list of the frequencies of the most common values,
i.e., number of occurrences of each divided by total number of rows.
(Null when <code class="structfield">most_common_vals</code> is.)
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">histogram_bounds</code> <code class="type">anyarray</code>
</p>
<p>
A list of values that divide the expression's values into groups of
approximately equal population. The values in
<code class="structfield">most_common_vals</code>, if present, are omitted from this
histogram calculation. (This expression is null if the expression data type
does not have a <code class="literal"><</code> operator or if the
<code class="structfield">most_common_vals</code> list accounts for the entire
population.)
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">correlation</code> <code class="type">float4</code>
</p>
<p>
Statistical correlation between physical row ordering and
logical ordering of the expression values. This ranges from -1 to +1.
When the value is near -1 or +1, an index scan on the expression will
be estimated to be cheaper than when it is near zero, due to reduction
of random access to the disk. (This expression is null if the expression's
data type does not have a <code class="literal"><</code> operator.)
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">most_common_elems</code> <code class="type">anyarray</code>
</p>
<p>
A list of non-null element values most often appearing within values of
the expression. (Null for scalar types.)
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">most_common_elem_freqs</code> <code class="type">float4[]</code>
</p>
<p>
A list of the frequencies of the most common element values, i.e., the
fraction of rows containing at least one instance of the given value.
Two or three additional values follow the per-element frequencies;
these are the minimum and maximum of the preceding per-element
frequencies, and optionally the frequency of null elements.
(Null when <code class="structfield">most_common_elems</code> is.)
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">elem_count_histogram</code> <code class="type">float4[]</code>
</p>
<p>
A histogram of the counts of distinct non-null element values within the
values of the expression, followed by the average number of distinct
non-null elements. (Null for scalar types.)
</p></td></tr></tbody></table></div></div><br class="table-break" /><p>
The maximum number of entries in the array fields can be controlled on a
column-by-column basis using the <a class="link" href="sql-altertable.html" title="ALTER TABLE"><code class="command">ALTER
TABLE SET STATISTICS</code></a> command, or globally by setting the
<a class="xref" href="runtime-config-query.html#GUC-DEFAULT-STATISTICS-TARGET">default_statistics_target</a> run-time parameter.
</p></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="view-pg-stats-ext.html" title="52.90. pg_stats_ext">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="view-pg-tables.html" title="52.92. pg_tables">Next</a></td></tr><tr><td width="40%" align="left" valign="top">52.90. <code xmlns="http://www.w3.org/1999/xhtml" class="structname">pg_stats_ext</code> </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 14.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 52.92. <code xmlns="http://www.w3.org/1999/xhtml" class="structname">pg_tables</code></td></tr></table></div></body></html>
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