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<?xml version="1.0" encoding="ISO-8859-1"?>
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<refentry id="fn_sys_stat_histogram">
<refmeta>
<refentrytitle>sys_stat_histogram</refentrytitle>
<refmiscinfo>sql</refmiscinfo>
</refmeta>
<refnamediv>
<refname>sys_stat_histogram</refname>
<refpurpose>Collects a column value histogram for use in SQL optimization </refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis id="fsyn_sys_stat_histogram">
<funcprototype id="fproto_sys_stat_histogram">
<funcdef><function>sys_stat_histogram</function></funcdef>
<paramdef>in <parameter>table_name</parameter> varchar</paramdef>
<paramdef>in <parameter>column_name</parameter> varchar</paramdef>
<paramdef>in <parameter>n_buckets</parameter> integer</paramdef>
<paramdef><optional>in <parameter>prec</parameter> integer</optional></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 id="desc"><title>Description</title>
<para>
This function collects (or updates) values distribution data for a given column.
</para>
<para>
It splits the sorted column values in n_buckets intervals and collects the last value of each interval.
The values are then inserted into the SYS_COL_HIST table.
</para>
<para>
If the table in question has not been analyzed, then it calls SYS_STAT_ANALYZE for the table.
</para>
<para>
The histograms are then used by the Optimized SQL compiler. All the cached compilations are
discarded, because some of them may compile differently in the light of the new data.
</para>
</refsect1>
<refsect1 id="params"><title>Parameters</title>
<refsect2><title>table_name</title>
<para>The full name of the table exactly as in the KEY_TABLE column of SYS_KEYS.</para></refsect2>
<refsect2><title>column_name</title>
<para>The full name of the column exactly as in the COLUMN column in SYS_COLS.</para></refsect2>
<refsect2><title>n_buckets</title>
<para>How much intervals to form. If more intervals are available, the estimation
of column predicates costs is more precise.
</para></refsect2>
<refsect2><title>prec</title>
<para>The density of the rows examined. Defaults to 1 (all the rows)</para></refsect2>
</refsect1>
<!--
<refsect1 id="errors"><title>Errors</title>
<table><title>Errors signalled by sys_stat_histogram</title>
<tgroup cols="4">
<thead>
<row><entry>SQL State</entry><entry>Error Code</entry><entry>Error Text</entry><entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><errorcode></errorcode></entry>
<entry><errorcode></errorcode></entry>
<entry><errorname></errorname></entry>
<entry></entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
-->
<refsect1 id="seealso"><title>See Also</title>
<para><link linkend="fn_SYS_DB_STAT"><function>SYS_DB_STAT()</function></link></para>
<para><link linkend="fn_sys_stat_analyze">sys_stat_analyze</link></para>
</refsect1>
</refentry>
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