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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >pg_statistic</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="System Catalogs" HREF="catalogs.html"><LINK REL="PREVIOUS" TITLE="pg_shseclabel" HREF="catalog-pg-shseclabel.html"><LINK REL="NEXT" TITLE="pg_tablespace" HREF="catalog-pg-tablespace.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2017-11-06T22:43:11"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="pg_shseclabel" HREF="catalog-pg-shseclabel.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="catalogs.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 45. System Catalogs</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="pg_tablespace" HREF="catalog-pg-tablespace.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="CATALOG-PG-STATISTIC" >45.42. <TT CLASS="STRUCTNAME" >pg_statistic</TT ></A ></H1 ><P > The catalog <TT CLASS="STRUCTNAME" >pg_statistic</TT > stores statistical data about the contents of the database. Entries are created by <A HREF="sql-analyze.html" >ANALYZE</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 <TT CLASS="STRUCTFIELD" >stainherit</TT > = <TT CLASS="LITERAL" >false</TT >, for each table column that has been analyzed. If the table has inheritance children, a second entry with <TT CLASS="STRUCTFIELD" >stainherit</TT > = <TT CLASS="LITERAL" >true</TT > is also created. This row represents the column's statistics over the inheritance tree, i.e., statistics for the data you'd see with <TT CLASS="LITERAL" >SELECT <TT CLASS="REPLACEABLE" ><I >column</I ></TT > FROM <TT CLASS="REPLACEABLE" ><I >table</I ></TT >*</TT >, whereas the <TT CLASS="STRUCTFIELD" >stainherit</TT > = <TT CLASS="LITERAL" >false</TT > row represents the results of <TT CLASS="LITERAL" >SELECT <TT CLASS="REPLACEABLE" ><I >column</I ></TT > FROM ONLY <TT CLASS="REPLACEABLE" ><I >table</I ></TT ></TT >. </P ><P > <TT CLASS="STRUCTNAME" >pg_statistic</TT > also stores statistical data about the values of index expressions. These are described as if they were actual data columns; in particular, <TT CLASS="STRUCTFIELD" >starelid</TT > 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 <TT CLASS="STRUCTFIELD" >stainherit</TT > = <TT CLASS="LITERAL" >false</TT >. </P ><P > Since different kinds of statistics might be appropriate for different kinds of data, <TT CLASS="STRUCTNAME" >pg_statistic</TT > 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 <TT CLASS="STRUCTNAME" >pg_statistic</TT >. Everything else is stored in <SPAN CLASS="QUOTE" >"slots"</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 <TT CLASS="FILENAME" >src/include/catalog/pg_statistic.h</TT >. </P ><P > <TT CLASS="STRUCTNAME" >pg_statistic</TT > 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 HREF="view-pg-stats.html" ><TT CLASS="STRUCTNAME" >pg_stats</TT ></A > is a publicly readable view on <TT CLASS="STRUCTNAME" >pg_statistic</TT > that only exposes information about those tables that are readable by the current user. </P ><DIV CLASS="TABLE" ><A NAME="AEN92716" ></A ><P ><B >Table 45-42. <TT CLASS="STRUCTNAME" >pg_statistic</TT > Columns</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Type</TH ><TH >References</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="STRUCTFIELD" >starelid</TT ></TD ><TD ><TT CLASS="TYPE" >oid</TT ></TD ><TD ><TT CLASS="LITERAL" ><A HREF="catalog-pg-class.html" ><TT CLASS="STRUCTNAME" >pg_class</TT ></A >.oid</TT ></TD ><TD >The table or index that the described column belongs to</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >staattnum</TT ></TD ><TD ><TT CLASS="TYPE" >int2</TT ></TD ><TD ><TT CLASS="LITERAL" ><A HREF="catalog-pg-attribute.html" ><TT CLASS="STRUCTNAME" >pg_attribute</TT ></A >.attnum</TT ></TD ><TD >The number of the described column</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >stainherit</TT ></TD ><TD ><TT CLASS="TYPE" >bool</TT ></TD ><TD > </TD ><TD >If true, the stats include inheritance child columns, not just the values in the specified relation</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >stanullfrac</TT ></TD ><TD ><TT CLASS="TYPE" >float4</TT ></TD ><TD > </TD ><TD >The fraction of the column's entries that are null</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >stawidth</TT ></TD ><TD ><TT CLASS="TYPE" >int4</TT ></TD ><TD > </TD ><TD >The average stored width, in bytes, of nonnull entries</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >stadistinct</TT ></TD ><TD ><TT CLASS="TYPE" >float4</TT ></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 <TT CLASS="STRUCTFIELD" >stadistinct</TT > = -0.4. A zero value means the number of distinct values is unknown. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >stakind<TT CLASS="REPLACEABLE" ><I >N</I ></TT ></TT ></TD ><TD ><TT CLASS="TYPE" >int2</TT ></TD ><TD > </TD ><TD > A code number indicating the kind of statistics stored in the <TT CLASS="REPLACEABLE" ><I >N</I ></TT >th <SPAN CLASS="QUOTE" >"slot"</SPAN > of the <TT CLASS="STRUCTNAME" >pg_statistic</TT > row. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >staop<TT CLASS="REPLACEABLE" ><I >N</I ></TT ></TT ></TD ><TD ><TT CLASS="TYPE" >oid</TT ></TD ><TD ><TT CLASS="LITERAL" ><A HREF="catalog-pg-operator.html" ><TT CLASS="STRUCTNAME" >pg_operator</TT ></A >.oid</TT ></TD ><TD > An operator used to derive the statistics stored in the <TT CLASS="REPLACEABLE" ><I >N</I ></TT >th <SPAN CLASS="QUOTE" >"slot"</SPAN >. For example, a histogram slot would show the <TT CLASS="LITERAL" ><</TT > operator that defines the sort order of the data. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >stanumbers<TT CLASS="REPLACEABLE" ><I >N</I ></TT ></TT ></TD ><TD ><TT CLASS="TYPE" >float4[]</TT ></TD ><TD > </TD ><TD > Numerical statistics of the appropriate kind for the <TT CLASS="REPLACEABLE" ><I >N</I ></TT >th <SPAN CLASS="QUOTE" >"slot"</SPAN >, or null if the slot kind does not involve numerical values </TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >stavalues<TT CLASS="REPLACEABLE" ><I >N</I ></TT ></TT ></TD ><TD ><TT CLASS="TYPE" >anyarray</TT ></TD ><TD > </TD ><TD > Column data values of the appropriate kind for the <TT CLASS="REPLACEABLE" ><I >N</I ></TT >th <SPAN CLASS="QUOTE" >"slot"</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 <TT CLASS="TYPE" >anyarray</TT >. </TD ></TR ></TBODY ></TABLE ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="catalog-pg-shseclabel.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="catalog-pg-tablespace.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><TT CLASS="STRUCTNAME" >pg_shseclabel</TT ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="catalogs.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><TT CLASS="STRUCTNAME" >pg_tablespace</TT ></TD ></TR ></TABLE ></DIV ></BODY ></HTML >