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<?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 16.2 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> <a href="#CATALOG-PG-ATTRIBUTE" class="id_link">#</a></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">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">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">attndims</code> <code class="type">int2</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">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">int2</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">attstattarget</code> <code class="type">int2</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">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 16.2 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>
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