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><A
NAME="CATALOG-PG-STATISTIC"
>44.34. <TT
CLASS="STRUCTNAME"
>pg_statistic</TT
></A
></H1
><A
NAME="AEN77311"
></A
><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"
><I
>ANALYZE</I
></A
>
and subsequently used by the query planner. There is one entry for
each table column that has been analyzed. Note that all the
statistical data is inherently approximate, even assuming that it
is up-to-date.
</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.
</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="AEN77329"
></A
><P
><B
>Table 44-34. <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"
>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 fraction of the number
of rows in the table (for example, a column in which values appear about
twice on the average could be represented by <TT
CLASS="STRUCTFIELD"
>stadistinct</TT
> = -0.5).
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, so there
is no way to define these columns' type more specifically than
<TT
CLASS="TYPE"
>anyarray</TT
>
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