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
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
|
<?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>53.7. pg_attribute</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-attrdef.html" title="53.6. pg_attrdef" /><link rel="next" href="catalog-pg-authid.html" title="53.8. pg_authid" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">53.7. <code class="structname">pg_attribute</code></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="catalog-pg-attrdef.html" title="53.6. pg_attrdef">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-authid.html" title="53.8. pg_authid">Next</a></td></tr></table><hr /></div><div class="sect1" id="CATALOG-PG-ATTRIBUTE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">53.7. <code class="structname">pg_attribute</code></h2></div></div></div><a id="id-1.10.4.9.2" class="indexterm"></a><p>
The catalog <code class="structname">pg_attribute</code> stores information about
table columns. There will be exactly one
<code class="structname">pg_attribute</code> row for every column in every
table in the database. (There will also be attribute entries for
indexes, and indeed all objects that have
<a class="link" href="catalog-pg-class.html" title="53.11. pg_class"><code class="structname">pg_class</code></a>
entries.)
</p><p>
The term attribute is equivalent to column and is used for
historical reasons.
</p><div class="table" id="id-1.10.4.9.5"><p class="title"><strong>Table 53.7. <code class="structname">pg_attribute</code> Columns</strong></p><div class="table-contents"><table class="table" summary="pg_attribute 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">attrelid</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 this column belongs to
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attname</code> <code class="type">name</code>
</p>
<p>
The column name
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">atttypid</code> <code class="type">oid</code>
(references <a class="link" href="catalog-pg-type.html" title="53.64. pg_type"><code class="structname">pg_type</code></a>.<code class="structfield">oid</code>)
</p>
<p>
The data type of this column (zero for a dropped column)
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attstattarget</code> <code class="type">int4</code>
</p>
<p>
<code class="structfield">attstattarget</code> controls the level of detail
of statistics accumulated for this column by
<a class="link" href="sql-analyze.html" title="ANALYZE"><code class="command">ANALYZE</code></a>.
A zero value indicates that no statistics should be collected.
A negative value says to use the system default statistics target.
The exact meaning of positive values is data type-dependent.
For scalar data types, <code class="structfield">attstattarget</code>
is both the target number of <span class="quote">“<span class="quote">most common values</span>”</span>
to collect, and the target number of histogram bins to create.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attlen</code> <code class="type">int2</code>
</p>
<p>
A copy of <code class="literal">pg_type.typlen</code> of this column's
type
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attnum</code> <code class="type">int2</code>
</p>
<p>
The number of the column. Ordinary columns are numbered from 1
up. System columns, such as <code class="structfield">ctid</code>,
have (arbitrary) negative numbers.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attndims</code> <code class="type">int4</code>
</p>
<p>
Number of dimensions, if the column is an array type; otherwise 0.
(Presently, the number of dimensions of an array is not enforced,
so any nonzero value effectively means <span class="quote">“<span class="quote">it's an array</span>”</span>.)
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attcacheoff</code> <code class="type">int4</code>
</p>
<p>
Always -1 in storage, but when loaded into a row descriptor
in memory this might be updated to cache the offset of the attribute
within the row
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">atttypmod</code> <code class="type">int4</code>
</p>
<p>
<code class="structfield">atttypmod</code> records type-specific data
supplied at table creation time (for example, the maximum
length of a <code class="type">varchar</code> column). It is passed to
type-specific input functions and length coercion functions.
The value will generally be -1 for types that do not need <code class="structfield">atttypmod</code>.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attbyval</code> <code class="type">bool</code>
</p>
<p>
A copy of <code class="literal">pg_type.typbyval</code> of this column's type
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attalign</code> <code class="type">char</code>
</p>
<p>
A copy of <code class="literal">pg_type.typalign</code> of this column's type
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attstorage</code> <code class="type">char</code>
</p>
<p>
Normally a copy of <code class="literal">pg_type.typstorage</code> of this
column's type. For TOAST-able data types, this can be altered
after column creation to control storage policy.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attcompression</code> <code class="type">char</code>
</p>
<p>
The current compression method of the column. Typically this is
<code class="literal">'\0'</code> to specify use of the current default setting
(see <a class="xref" href="runtime-config-client.html#GUC-DEFAULT-TOAST-COMPRESSION">default_toast_compression</a>). Otherwise,
<code class="literal">'p'</code> selects pglz compression, while
<code class="literal">'l'</code> selects <span class="productname">LZ4</span>
compression. However, this field is ignored
whenever <code class="structfield">attstorage</code> does not allow
compression.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attnotnull</code> <code class="type">bool</code>
</p>
<p>
This represents a not-null constraint.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">atthasdef</code> <code class="type">bool</code>
</p>
<p>
This column has a default expression or generation expression, in which
case there will be a corresponding entry in the
<a class="link" href="catalog-pg-attrdef.html" title="53.6. pg_attrdef"><code class="structname">pg_attrdef</code></a> catalog that actually defines the
expression. (Check <code class="structfield">attgenerated</code> to
determine whether this is a default or a generation expression.)
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">atthasmissing</code> <code class="type">bool</code>
</p>
<p>
This column has a value which is used where the column is entirely
missing from the row, as happens when a column is added with a
non-volatile <code class="literal">DEFAULT</code> value after the row is created.
The actual value used is stored in the
<code class="structfield">attmissingval</code> column.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attidentity</code> <code class="type">char</code>
</p>
<p>
If a zero byte (<code class="literal">''</code>), then not an identity column.
Otherwise, <code class="literal">a</code> = generated
always, <code class="literal">d</code> = generated by default.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attgenerated</code> <code class="type">char</code>
</p>
<p>
If a zero byte (<code class="literal">''</code>), then not a generated column.
Otherwise, <code class="literal">s</code> = stored. (Other values might be added
in the future.)
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attisdropped</code> <code class="type">bool</code>
</p>
<p>
This column has been dropped and is no longer valid. A dropped
column is still physically present in the table, but is
ignored by the parser and so cannot be accessed via SQL.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attislocal</code> <code class="type">bool</code>
</p>
<p>
This column is defined locally in the relation. Note that a column can
be locally defined and inherited simultaneously.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attinhcount</code> <code class="type">int4</code>
</p>
<p>
The number of direct ancestors this column has. A column with a
nonzero number of ancestors cannot be dropped nor renamed.
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attcollation</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 defined collation of the column, or zero if the column is
not of a collatable data type
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attacl</code> <code class="type">aclitem[]</code>
</p>
<p>
Column-level access privileges, if any have been granted specifically
on this column
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attoptions</code> <code class="type">text[]</code>
</p>
<p>
Attribute-level options, as <span class="quote">“<span class="quote">keyword=value</span>”</span> strings
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attfdwoptions</code> <code class="type">text[]</code>
</p>
<p>
Attribute-level foreign data wrapper options, as <span class="quote">“<span class="quote">keyword=value</span>”</span> strings
</p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition">
<code class="structfield">attmissingval</code> <code class="type">anyarray</code>
</p>
<p>
This column has a one element array containing the value used when the
column is entirely missing from the row, as happens when the column is
added with a non-volatile <code class="literal">DEFAULT</code> value after the
row is created. The value is only used when
<code class="structfield">atthasmissing</code> is true. If there is no value
the column is null.
</p></td></tr></tbody></table></div></div><br class="table-break" /><p>
In a dropped column's <code class="structname">pg_attribute</code> entry,
<code class="structfield">atttypid</code> is reset to zero, but
<code class="structfield">attlen</code> and the other fields copied from
<a class="link" href="catalog-pg-type.html" title="53.64. pg_type"><code class="structname">pg_type</code></a> are still valid. This arrangement is needed
to cope with the situation where the dropped column's data type was
later dropped, and so there is no <code class="structname">pg_type</code> row anymore.
<code class="structfield">attlen</code> and the other fields can be used
to interpret the contents of a row of the table.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="catalog-pg-attrdef.html" title="53.6. pg_attrdef">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-authid.html" title="53.8. pg_authid">Next</a></td></tr><tr><td width="40%" align="left" valign="top">53.6. <code class="structname">pg_attrdef</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"> 53.8. <code class="structname">pg_authid</code></td></tr></table></div></body></html>
|
