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><H1
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><A
NAME="CATALOG-PG-ATTRIBUTE"
>3.7. pg_attribute</A
></H1
><P
> <TT
CLASS="STRUCTNAME"
>pg_attribute</TT
> stores information about
table columns. There will be exactly one
<TT
CLASS="STRUCTNAME"
>pg_attribute</TT
> row for every column in every
table in the database. (There will also be attribute entries for
indexes and other objects. See <TT
CLASS="STRUCTNAME"
>pg_class</TT
>.)
</P
><P
> The term attribute is equivalent to column and is used for
historical reasons.
</P
><DIV
CLASS="TABLE"
><A
NAME="AEN52696"
></A
><P
><B
>Table 3-7. pg_attribute Columns</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><THEAD
><TR
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Name</TH
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Type</TH
><TH
ALIGN="LEFT"
VALIGN="TOP"
>References</TH
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attrelid</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>pg_class.oid</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>The table this column belongs to</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attname</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>name</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Column name</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>atttypid</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>pg_type.oid</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>The data type of this column</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attstattarget</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <TT
CLASS="STRUCTFIELD"
>attstattarget</TT
> controls the level of detail
of statistics accumulated for this column by
<TT
CLASS="COMMAND"
>ANALYZE</TT
>.
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 datatype-dependent.
For scalar datatypes, <TT
CLASS="STRUCTFIELD"
>attstattarget</TT
>
is both the target number of <SPAN
CLASS="QUOTE"
>"most common values"</SPAN
>
to collect, and the target number of histogram bins to create.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attlen</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>int2</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> This is a copy of
<TT
CLASS="STRUCTNAME"
>pg_type</TT
>.<TT
CLASS="STRUCTFIELD"
>typlen</TT
>
of this column's type.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attnum</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>int2</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> The number of the column. Ordinary columns are numbered from 1
up. System columns, such as <TT
CLASS="STRUCTFIELD"
>oid</TT
>,
have (arbitrary) negative numbers.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attndims</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> 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"
>"it's an array"</SPAN
>.)
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attcacheoff</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> Always -1 in storage, but when loaded into a tuple descriptor
in memory this may be updated to cache the offset of the attribute
within the tuple.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>atttypmod</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <TT
CLASS="STRUCTFIELD"
>atttypmod</TT
> records type-specific data
supplied at table creation time (for example, the maximum
length of a <TT
CLASS="TYPE"
>varchar</TT
> 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 typmod.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attbyval</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> A copy of
<TT
CLASS="STRUCTNAME"
>pg_type</TT
>.<TT
CLASS="STRUCTFIELD"
>typbyval</TT
>
of this column's type
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attstorage</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>char</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> Normally a copy of
<TT
CLASS="STRUCTNAME"
>pg_type</TT
>.<TT
CLASS="STRUCTFIELD"
>typstorage</TT
>
of this column's type. For TOASTable datatypes, this can be altered
after column creation to control storage policy.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attisset</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> If true, this attribute is a set. In that case, what is really
stored in the attribute is the OID of a tuple in the
<TT
CLASS="STRUCTNAME"
>pg_proc</TT
> catalog. The
<TT
CLASS="STRUCTNAME"
>pg_proc</TT
> tuple contains the query
string that defines this set - i.e., the query to run to get
the set. So the <TT
CLASS="STRUCTFIELD"
>atttypid</TT
> (see
above) refers to the type returned by this query, but the
actual length of this attribute is the length (size) of an
<TT
CLASS="TYPE"
>oid</TT
>. --- At least this is the theory. All this
is probably quite broken these days.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attalign</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>char</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> A copy of
<TT
CLASS="STRUCTNAME"
>pg_type</TT
>.<TT
CLASS="STRUCTFIELD"
>typalign</TT
>
of this column's type
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attnotnull</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> This represents a NOT NULL constraint. It is possible to
change this field to enable or disable the constraint.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>atthasdef</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> This column has a default value, in which case there will be a
corresponding entry in the <TT
CLASS="STRUCTNAME"
>pg_attrdef</TT
>
catalog that actually defines the value.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attisdropped</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> 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.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attislocal</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> This column is defined locally in the relation. Note that a column may
be locally defined and inherited simultaneously.
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>attinhcount</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> The number of direct ancestors this column has. A column with a
nonzero number of ancestors cannot be dropped nor renamed.
</TD
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