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>CREATE FOREIGN DATA WRAPPER</TITLE
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><H1
><A
NAME="SQL-CREATEFOREIGNDATAWRAPPER"
></A
>CREATE FOREIGN DATA WRAPPER</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN68277"
></A
><H2
>Name</H2
>CREATE FOREIGN DATA WRAPPER -- define a new foreign-data wrapper</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN68282"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>CREATE FOREIGN DATA WRAPPER <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
>
[ HANDLER <TT
CLASS="REPLACEABLE"
><I
>handler_function</I
></TT
> | NO HANDLER ]
[ VALIDATOR <TT
CLASS="REPLACEABLE"
><I
>validator_function</I
></TT
> | NO VALIDATOR ]
[ OPTIONS ( <TT
CLASS="REPLACEABLE"
><I
>option</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>' [, ... ] ) ]</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN68289"
></A
><H2
>Description</H2
><P
> <TT
CLASS="COMMAND"
>CREATE FOREIGN DATA WRAPPER</TT
> creates a new
foreign-data wrapper. The user who defines a foreign-data wrapper
becomes its owner.
</P
><P
> The foreign-data wrapper name must be unique within the database.
</P
><P
> Only superusers can create foreign-data wrappers.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN68295"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
></DT
><DD
><P
> The name of the foreign-data wrapper to be created.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>HANDLER <TT
CLASS="REPLACEABLE"
><I
>handler_function</I
></TT
></TT
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>handler_function</I
></TT
> is the
name of a previously registered function that will be called to
retrieve the execution functions for foreign tables.
The handler function must take no arguments, and
its return type must be <TT
CLASS="TYPE"
>fdw_handler</TT
>.
</P
><P
> It is possible to create a foreign-data wrapper with no handler
function, but foreign tables using such a wrapper can only be declared,
not accessed.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>VALIDATOR <TT
CLASS="REPLACEABLE"
><I
>validator_function</I
></TT
></TT
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>validator_function</I
></TT
> is the
name of a previously registered function that will be called to
check the generic options given to the foreign-data wrapper, as
well as options for foreign servers and user mappings using the
foreign-data wrapper. If no validator function or <TT
CLASS="LITERAL"
>NO
VALIDATOR</TT
> is specified, then options will not be
checked at creation time. (Foreign-data wrappers will possibly
ignore or reject invalid option specifications at run time,
depending on the implementation.) The validator function must
take two arguments: one of type <TT
CLASS="TYPE"
>text[]</TT
>, which will
contain the array of options as stored in the system catalogs,
and one of type <TT
CLASS="TYPE"
>oid</TT
>, which will be the OID of the
system catalog containing the options. The return type is ignored;
the function should report invalid options using the
<CODE
CLASS="FUNCTION"
>ereport(ERROR)</CODE
> function.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>OPTIONS ( <TT
CLASS="REPLACEABLE"
><I
>option</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>' [, ... ] )</TT
></DT
><DD
><P
> This clause specifies options for the new foreign-data wrapper.
The allowed option names and values are specific to each foreign
data wrapper and are validated using the foreign-data wrapper's
validator function. Option names must be unique.
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN68330"
></A
><H2
>Notes</H2
><P
> At the moment, the foreign-data wrapper functionality is rudimentary.
There is no support for updating a foreign table, and optimization of
queries is primitive (and mostly left to the wrapper, too).
</P
><P
> There is one built-in foreign-data wrapper validator function
provided:
<TT
CLASS="FILENAME"
>postgresql_fdw_validator</TT
>, which accepts
options corresponding to <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> connection
parameters.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN68336"
></A
><H2
>Examples</H2
><P
> Create a useless foreign-data wrapper <TT
CLASS="LITERAL"
>dummy</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FOREIGN DATA WRAPPER dummy;</PRE
><P>
</P
><P
> Create a foreign-data wrapper <TT
CLASS="LITERAL"
>file</TT
> with
handler function <TT
CLASS="LITERAL"
>file_fdw_handler</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FOREIGN DATA WRAPPER file HANDLER file_fdw_handler;</PRE
><P>
</P
><P
> Create a foreign-data wrapper <TT
CLASS="LITERAL"
>mywrapper</TT
> with some
options:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FOREIGN DATA WRAPPER mywrapper
OPTIONS (debug 'true');</PRE
><P></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN68348"
></A
><H2
>Compatibility</H2
><P
> <TT
CLASS="COMMAND"
>CREATE FOREIGN DATA WRAPPER</TT
> conforms to ISO/IEC
9075-9 (SQL/MED), with the exception that the <TT
CLASS="LITERAL"
>HANDLER</TT
>
and <TT
CLASS="LITERAL"
>VALIDATOR</TT
> clauses are extensions and the standard
clauses <TT
CLASS="LITERAL"
>LIBRARY</TT
> and <TT
CLASS="LITERAL"
>LANGUAGE</TT
>
are not implemented in PostgreSQL.
</P
><P
> Note, however, that the SQL/MED functionality as a whole is not yet
conforming.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN68357"
></A
><H2
>See Also</H2
><A
HREF="sql-alterforeigndatawrapper.html"
>ALTER FOREIGN DATA WRAPPER</A
>, <A
HREF="sql-dropforeigndatawrapper.html"
>DROP FOREIGN DATA WRAPPER</A
>, <A
HREF="sql-createserver.html"
>CREATE SERVER</A
>, <A
HREF="sql-createusermapping.html"
>CREATE USER MAPPING</A
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