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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>9.29. Statistics Information 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="functions-event-triggers.html" title="9.28. Event Trigger Functions" /><link rel="next" href="typeconv.html" title="Chapter 10. Type Conversion" /></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">9.29. Statistics Information Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-event-triggers.html" title="9.28. Event Trigger Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><th width="60%" align="center">Chapter 9. Functions and Operators</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="typeconv.html" title="Chapter 10. Type Conversion">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="FUNCTIONS-STATISTICS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.29. Statistics Information Functions</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="functions-statistics.html#FUNCTIONS-STATISTICS-MCV">9.29.1. Inspecting MCV Lists</a></span></dt></dl></div><a id="id-1.5.8.34.2" class="indexterm"></a><p>
- <span class="productname">PostgreSQL</span> provides a function to inspect complex
- statistics defined using the <code class="command">CREATE STATISTICS</code> command.
- </p><div class="sect2" id="FUNCTIONS-STATISTICS-MCV"><div class="titlepage"><div><div><h3 class="title">9.29.1. Inspecting MCV Lists</h3></div></div></div><a id="id-1.5.8.34.4.2" class="indexterm"></a><p>
- <code class="function">pg_mcv_list_items</code> returns a list of all items
- stored in a multi-column <acronym class="acronym">MCV</acronym> list, and returns the
- following columns:
-
- </p><div class="informaltable"><table class="informaltable" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="literal">index</code></td><td><code class="type">int</code></td><td>index of the item in the <acronym class="acronym">MCV</acronym> list</td></tr><tr><td><code class="literal">values</code></td><td><code class="type">text[]</code></td><td>values stored in the MCV item</td></tr><tr><td><code class="literal">nulls</code></td><td><code class="type">boolean[]</code></td><td>flags identifying <code class="literal">NULL</code> values</td></tr><tr><td><code class="literal">frequency</code></td><td><code class="type">double precision</code></td><td>frequency of this <acronym class="acronym">MCV</acronym> item</td></tr><tr><td><code class="literal">base_frequency</code></td><td><code class="type">double precision</code></td><td>base frequency of this <acronym class="acronym">MCV</acronym> item</td></tr></tbody></table></div><p>
- </p><p>
- The <code class="function">pg_mcv_list_items</code> function can be used like this:
-
- </p><pre class="programlisting">
- SELECT m.* FROM pg_statistic_ext join pg_statistic_ext_data on (oid = stxoid),
- pg_mcv_list_items(stxdmcv) m WHERE stxname = 'stts';
- </pre><p>
-
- Values of the <code class="type">pg_mcv_list</code> can be obtained only from the
- <code class="literal">pg_statistic_ext_data.stxdmcv</code> column.
- </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="functions-event-triggers.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="functions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="typeconv.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">9.28. Event Trigger Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 10. Type Conversion</td></tr></table></div></body></html>
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