1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
|
<?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>53.51. pg_statistic</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="catalog-pg-shseclabel.html" title="53.50. pg_shseclabel" /><link rel="next" href="catalog-pg-statistic-ext.html" title="53.52. pg_statistic_ext" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">53.51. <code class="structname">pg_statistic</code></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="catalog-pg-shseclabel.html" title="53.50. pg_shseclabel">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="catalogs.html" title="Chapter 53. System Catalogs">Up</a></td><th width="60%" align="center">Chapter 53. System Catalogs</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.7 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="catalog-pg-statistic-ext.html" title="53.52. pg_statistic_ext">Next</a></td></tr></table><hr /></div><div class="sect1" id="CATALOG-PG-STATISTIC"><div class="titlepage"><div><div><h2 class="title" style="clear: both">53.51. <code class="structname">pg_statistic</code></h2></div></div></div><a id="id-1.10.4.53.2" class="indexterm"></a><p>
The catalog <code class="structname">pg_statistic</code> stores
statistical data about the contents of the database. Entries are
created by <a class="link" href="sql-analyze.html" title="ANALYZE"><code class="command">ANALYZE</code></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 <code class="structfield">stainherit</code> =
<code class="literal">false</code>, for each table column that has been analyzed.
If the table has inheritance children or partitions, a second entry with
<code class="structfield">stainherit</code> = <code class="literal">true</code> is also created. This row
represents the column's statistics over the inheritance tree, i.e.,
statistics for the data you'd see with
<code class="literal">SELECT <em class="replaceable"><code>column</code></em> FROM <em class="replaceable"><code>table</code></em>*</code>,
whereas the <code class="structfield">stainherit</code> = <code class="literal">false</code> row represents
the results of
<code class="literal">SELECT <em class="replaceable"><code>column</code></em> FROM ONLY <em class="replaceable"><code>table</code></em></code>.
</p><p>
<code class="structname">pg_statistic</code> also stores statistical data about
the values of index expressions. These are described as if they were
actual data columns; in particular, <code class="structfield">starelid</code>
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 <code class="structfield">stainherit</code> = <code class="literal">false</code>.
</p><p>
Since different kinds of statistics might be appropriate for different
kinds of data, <code class="structname">pg_statistic</code> 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 <code class="structname">pg_statistic</code>. Everything else
is stored in <span class="quote">“<span class="quote">slots</span>”</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
<code class="filename">src/include/catalog/pg_statistic.h</code>.
</p><p>
<code class="structname">pg_statistic</code> 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 class="link" href="view-pg-stats.html" title="54.27. pg_stats"><code class="structname">pg_stats</code></a>
is a publicly readable view on
<code class="structname">pg_statistic</code> that only exposes information
about those tables that are readable by the current user.
</p><div class="table" id="id-1.10.4.53.8"><p class="title"><strong>Table 53.51. <code class="structname">pg_statistic</code> Columns</strong></p><div class="table-contents"><table class="table" summary="pg_statistic 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">starelid</code> <code class="type">oid</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">oid</code>)
</p>
<p>
The table or index that the described column belongs to
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">staattnum</code> <code class="type">int2</code>
(references <a class="link" href="catalog-pg-attribute.html" title="53.7. pg_attribute"><code class="structname">pg_attribute</code></a>.<code class="structfield">attnum</code>)
</p>
<p>
The number of the described column
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">stainherit</code> <code class="type">bool</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">stanullfrac</code> <code class="type">float4</code>
</p>
<p>
The fraction of the column's entries that are null
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">stawidth</code> <code class="type">int4</code>
</p>
<p>
The average stored width, in bytes, of nonnull entries
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">stadistinct</code> <code class="type">float4</code>
</p>
<p>
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 <code class="structfield">stadistinct</code> = -0.4.
A zero value means the number of distinct values is unknown.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">stakind<em class="replaceable"><code>N</code></em></code> <code class="type">int2</code>
</p>
<p>
A code number indicating the kind of statistics stored in the
<em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span> of the
<code class="structname">pg_statistic</code> row.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">staop<em class="replaceable"><code>N</code></em></code> <code class="type">oid</code>
(references <a class="link" href="catalog-pg-operator.html" title="53.34. pg_operator"><code class="structname">pg_operator</code></a>.<code class="structfield">oid</code>)
</p>
<p>
An operator used to derive the statistics stored in the
<em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span>. For example, a
histogram slot would show the <code class="literal"><</code> operator
that defines the sort order of the data.
Zero if the statistics kind does not require an operator.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">stacoll<em class="replaceable"><code>N</code></em></code> <code class="type">oid</code>
(references <a class="link" href="catalog-pg-collation.html" title="53.12. pg_collation"><code class="structname">pg_collation</code></a>.<code class="structfield">oid</code>)
</p>
<p>
The collation used to derive the statistics stored in the
<em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span>. For example, a
histogram slot for a collatable column would show the collation that
defines the sort order of the data. Zero for noncollatable data.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">stanumbers<em class="replaceable"><code>N</code></em></code> <code class="type">float4[]</code>
</p>
<p>
Numerical statistics of the appropriate kind for the
<em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</span>, or null if the slot
kind does not involve numerical values
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">stavalues<em class="replaceable"><code>N</code></em></code> <code class="type">anyarray</code>
</p>
<p>
Column data values of the appropriate kind for the
<em class="replaceable"><code>N</code></em>th <span class="quote">“<span class="quote">slot</span>”</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 <code class="type">anyarray</code>.
</p></td></tr></tbody></table></div></div><br class="table-break" /></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="catalog-pg-shseclabel.html" title="53.50. pg_shseclabel">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="catalogs.html" title="Chapter 53. System Catalogs">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="catalog-pg-statistic-ext.html" title="53.52. pg_statistic_ext">Next</a></td></tr><tr><td width="40%" align="left" valign="top">53.50. <code class="structname">pg_shseclabel</code> </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.7 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 53.52. <code class="structname">pg_statistic_ext</code></td></tr></table></div></body></html>
|
