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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>54.29. 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="54.28. pg_stats_ext" /><link rel="next" href="view-pg-tables.html" title="54.30. pg_tables" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">54.29. <code 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="54.28. pg_stats_ext">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="views.html" title="Chapter 54. System Views">Up</a></td><th width="60%" align="center">Chapter 54. System Views</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="view-pg-tables.html" title="54.30. pg_tables">Next</a></td></tr></table><hr /></div><div class="sect1" id="VIEW-PG-STATS-EXT-EXPRS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">54.29. <code class="structname">pg_stats_ext_exprs</code> <a href="#VIEW-PG-STATS-EXT-EXPRS" class="id_link">#</a></h2></div></div></div><a id="id-1.10.5.33.2" 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="53.52. pg_statistic_ext"><code class="structname">pg_statistic_ext</code></a>
   and <a class="link" href="catalog-pg-statistic-ext-data.html" title="53.53. 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="53.52. pg_statistic_ext"><code class="structname">pg_statistic_ext</code></a> and <a class="link" href="catalog-pg-statistic-ext-data.html" title="53.53. 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-1.10.5.33.5"><p class="title"><strong>Table 54.29. <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="53.32. 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="53.11. 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="53.32. 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="53.52. 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="53.8. 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">inherited</code> <code class="type">bool</code>
       (references <a class="link" href="catalog-pg-statistic-ext-data.html" title="53.53. pg_statistic_ext_data"><code class="structname">pg_statistic_ext_data</code></a>.<code class="structfield">stxdinherit</code>)
      </p>
      <p>
       If true, the stats include values from child tables, not just the
       values in the specified relation
      </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">&lt;</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">&lt;</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 class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="view-pg-stats-ext.html" title="54.28. pg_stats_ext">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="views.html" title="Chapter 54. System Views">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="view-pg-tables.html" title="54.30. pg_tables">Next</a></td></tr><tr><td width="40%" align="left" valign="top">54.28. <code class="structname">pg_stats_ext</code> </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 54.30. <code class="structname">pg_tables</code></td></tr></table></div></body></html>