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<chapter id="datatype">
</row>
<row>
- <entry><type>oid</type></entry>
- <entry></entry>
- <entry>object identifier</entry>
- </row>
-
- <row>
<entry><type>path</type></entry>
<entry></entry>
<entry>open and closed geometric path in 2D plane</entry>
</sect1>
+ <sect1 id="datatype-oid">
+ <title>Object Identifier Types</title>
+
+ <indexterm zone="datatype-oid">
+ <primary>object identifier</primary>
+ <secondary>data type</secondary>
+ </indexterm>
+
+ <indexterm zone="datatype-oid">
+ <primary>oid</primary>
+ </indexterm>
+
+ <indexterm zone="datatype-oid">
+ <primary>regproc</primary>
+ </indexterm>
+
+ <indexterm zone="datatype-oid">
+ <primary>regprocedure</primary>
+ </indexterm>
+
+ <indexterm zone="datatype-oid">
+ <primary>regoper</primary>
+ </indexterm>
+
+ <indexterm zone="datatype-oid">
+ <primary>regoperator</primary>
+ </indexterm>
+
+ <indexterm zone="datatype-oid">
+ <primary>regclass</primary>
+ </indexterm>
+
+ <indexterm zone="datatype-oid">
+ <primary>regtype</primary>
+ </indexterm>
+
+ <para>
+ Object identifiers (OIDs) are used internally by
+ <productname>PostgreSQL</productname> as primary keys for various system
+ tables. Also, an OID system column is added to user-created tables
+ (unless <literal>WITHOUT OIDS</> is specified at table creation time).
+ Type <type>oid</> represents an object identifier. There are also
+ several aliases for <type>oid</>: <type>regproc</>, <type>regprocedure</>,
+ <type>regoper</>, <type>regoperator</>, <type>regclass</>,
+ and <type>regtype</>.
+ </para>
+
+ <para>
+ The <type>oid</> type is currently implemented as an unsigned four-byte
+ integer.
+ Therefore, it is not large enough to provide database-wide uniqueness
+ in large databases, or even in large individual tables. So, using a
+ user-created table's OID column as a primary key is discouraged.
+ OIDs are best used only for references to system tables.
+ </para>
+
+ <para>
+ The <type>oid</> type itself has few operations beyond comparison
+ (which is implemented as unsigned comparison). It can be cast to
+ integer, however, and then manipulated using the standard integer
+ operators. (Beware of possible signed-versus-unsigned confusion
+ if you do this.)
+ </para>
+
+ <para>
+ The <type>oid</> alias types have no operations of their own except
+ for specialized input and output routines. These routines are able
+ to accept and display symbolic names for system objects, rather than
+ the raw numeric value that type <type>oid</> would use. The alias
+ types allow simplified lookup of OID values for objects: for example,
+ one may write <literal>'mytable'::regclass</> to get the OID of table
+ <literal>mytable</>, rather than <literal>SELECT oid FROM pg_class WHERE
+ relname = 'mytable'</>. (In reality, a much more complicated SELECT would
+ be needed to deal with selecting the right OID when there are multiple
+ tables named <literal>mytable</> in different schemas.)
+ </para>
+
+ <para>
+ <table tocentry="1">
+ <title>Object Identifier Types</title>
+ <tgroup cols="4">
+ <thead>
+ <row>
+ <entry>Type name</entry>
+ <entry>References</entry>
+ <entry>Description</entry>
+ <entry>Examples</entry>
+ </row>
+ </thead>
+
+ <tbody>
+
+ <row>
+ <entry><type>oid</></entry>
+ <entry>any</entry>
+ <entry>Numeric object identifier</entry>
+ <entry>564182</entry>
+ </row>
+
+ <row>
+ <entry><type>regproc</></entry>
+ <entry>pg_proc</entry>
+ <entry>Function name</entry>
+ <entry>sum</entry>
+ </row>
+
+ <row>
+ <entry><type>regprocedure</></entry>
+ <entry>pg_proc</entry>
+ <entry>Function with argument types</entry>
+ <entry>sum(int4)</entry>
+ </row>
+
+ <row>
+ <entry><type>regoper</></entry>
+ <entry>pg_operator</entry>
+ <entry>Operator name</entry>
+ <entry>+</entry>
+ </row>
+
+ <row>
+ <entry><type>regoperator</></entry>
+ <entry>pg_operator</entry>
+ <entry>Operator with argument types</entry>
+ <entry>*(integer,integer) -(NONE,integer)</entry>
+ </row>
+
+ <row>
+ <entry><type>regclass</></entry>
+ <entry>pg_class</entry>
+ <entry>Relation name</entry>
+ <entry>pg_type</entry>
+ </row>
+
+ <row>
+ <entry><type>regtype</></entry>
+ <entry>pg_type</entry>
+ <entry>Type name</entry>
+ <entry>integer</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </para>
+
+ <para>
+ All of the alias types accept schema-qualified names, and will
+ display schema-qualified names on output if the object would not
+ be found in the current search path without being qualified.
+ The <type>regproc</> and <type>regoper</> alias types will only
+ accept input names that are unique (not overloaded), so they are
+ of limited use; for most uses <type>regprocedure</> or
+ <type>regoperator</> is more appropriate. For <type>regoperator</>,
+ unary operators are identified by writing NONE for the unused
+ operand.
+ </para>
+
+ </sect1>
+
</chapter>
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