<primary>internal</primary>

</indexterm>

<indexterm zone="datatype-pseudo">

<primary>unknown</primary>

</indexterm>

<indexterm zone="datatype-pseudo">

<primary>opaque</primary>

</indexterm>

<entry>Indicates that a function returns no value.</entry>

</row>

<row>

<entry><type>unknown</></entry>

<entry>Identifies a not-yet-resolved type, e.g. of an undecorated

string literal.</entry>

</row>

<row>

<entry><type>opaque</></entry>

<entry>An obsolete type name that formerly served all the above purposes.</entry>

<entry>An obsolete type name that formerly served many of the above

purposes.</entry>

</row>

</tbody>

</tgroup>

<para>

Another way to get the same effect is to use the <type>regclass</>

pseudo-type, which will print the table OID symbolically:

aliastype, which will print the table OID symbolically:

<programlisting>

SELECT c.tableoid::regclass, c.name, c.altitude

language such as C, using the version-1 interface, and registered

with <productname>PostgreSQL</productname> as taking no arguments

and returning the type <type>language_handler</type>. This

specialpseudotype identifies the function as a call handler and

specialpseudo-type identifies the function as a call handler and

prevents it from being called directly in SQL commands.

For more details on C language calling conventions and dynamic loading,

see <xref linkend="xfunc-c">.

number of parameter symbols (<literal>$</><replaceable>n</>)

used in the query string. Another special case is that a parameter's

type can be specified as <type>void</> (that is, the OID of the

<type>void</>pseudotype). This is meant to allow parameter symbols

<type>void</>pseudo-type). This is meant to allow parameter symbols

to be used for function parameters that are actually OUT parameters.

Ordinarily there is no context in which a <type>void</> parameter

could be used, but if such a parameter symbol appears in a function's

In some cases it is useful to define table functions that can

return different column sets depending on how they are invoked.

To support this, the table function can be declared as returning

thepseudotype <type>record</>. When such a function is used in

thepseudo-type <type>record</>. When such a function is used in

a query, the expected row structure must be specified in the

query itself, so that the system can know how to parse and plan

the query. This syntax looks like:

</para>

<para>

Depending on the implementation language it might also be allowed

to specify <quote>pseudotypes</> such as <type>cstring</>.

Pseudotypes indicate that the actual argument type is either

to specify <quote>pseudo-types</> such as <type>cstring</>.

Pseudo-types indicate that the actual argument type is either

incompletely specified, or outside the set of ordinary SQL data types.

</para>

<para>

can be a base, composite, or domain type,

or can reference the type of a table column.

Depending on the implementation language it might also be allowed

to specify <quote>pseudotypes</> such as <type>cstring</>.

to specify <quote>pseudo-types</> such as <type>cstring</>.

If the function is not supposed to return a value, specify

<type>void</> as the return type.

</para>

In <productname>PostgreSQL</productname> versions before 7.3, it

was customary to avoid creating a shell type at all, by replacing the

functions' forward references to the type name with the placeholder

pseudotype <type>opaque</>. The <type>cstring</> arguments and

pseudo-type <type>opaque</>. The <type>cstring</> arguments and

results also had to be declared as <type>opaque</> before 7.3. To

support loading of old dump files, <command>CREATE TYPE</> will

accept I/O functions declared using <type>opaque</>, but it will issue

charatt_typtype=get_typtype(atttypid);

Oidatt_typelem;

if (atttypid==UNKNOWNOID||

att_typtype==TYPTYPE_PSEUDO)

if (att_typtype==TYPTYPE_PSEUDO)

{

DATA(insertOID=704 (tintervalPGNSPPGUID12fbTft \054001025tintervalintintervalouttintervalrecvtintervalsend---ipf0-100_null__null__null_ ));

DESCR("(abstime,abstime), time interval");

#defineTINTERVALOID704

DATA(insertOID=705 (unknownPGNSPPGUID-2fbXft \054000unknowninunknownoutunknownrecvunknownsend---cpf0-100_null__null__null_ ));

DATA(insertOID=705 (unknownPGNSPPGUID-2fpXft \054000unknowninunknownoutunknownrecvunknownsend---cpf0-100_null__null__null_ ));

DESCR("");

#defineUNKNOWNOID705