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><H1
><A
NAME="SQL-CREATEFOREIGNTABLE"
></A
>CREATE FOREIGN TABLE</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN80143"
></A
><H2
>Name</H2
>CREATE FOREIGN TABLE -- define a new foreign table</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN80146"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>CREATE FOREIGN TABLE [ IF NOT EXISTS ] <TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
> ( [
{ <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>data_type</I
></TT
> [ OPTIONS ( <TT
CLASS="REPLACEABLE"
><I
>option</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>' [, ... ] ) ] [ COLLATE <TT
CLASS="REPLACEABLE"
><I
>collation</I
></TT
> ] [ <TT
CLASS="REPLACEABLE"
><I
>column_constraint</I
></TT
> [ ... ] ]
| <TT
CLASS="REPLACEABLE"
><I
>table_constraint</I
></TT
> }
[, ... ]
] )
[ INHERITS ( <TT
CLASS="REPLACEABLE"
><I
>parent_table</I
></TT
> [, ... ] ) ]
SERVER <TT
CLASS="REPLACEABLE"
><I
>server_name</I
></TT
>
[ OPTIONS ( <TT
CLASS="REPLACEABLE"
><I
>option</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>' [, ... ] ) ]
<SPAN
CLASS="phrase"
><SPAN
CLASS="PHRASE"
>where <TT
CLASS="REPLACEABLE"
><I
>column_constraint</I
></TT
> is:</SPAN
></SPAN
>
[ CONSTRAINT <TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
> ]
{ NOT NULL |
NULL |
CHECK ( <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ) [ NO INHERIT ] |
DEFAULT <TT
CLASS="REPLACEABLE"
><I
>default_expr</I
></TT
> }
<SPAN
CLASS="phrase"
><SPAN
CLASS="PHRASE"
>and <TT
CLASS="REPLACEABLE"
><I
>table_constraint</I
></TT
> is:</SPAN
></SPAN
>
[ CONSTRAINT <TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
> ]
CHECK ( <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ) [ NO INHERIT ]</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATEFOREIGNTABLE-DESCRIPTION"
></A
><H2
>Description</H2
><P
> <TT
CLASS="COMMAND"
>CREATE FOREIGN TABLE</TT
> creates a new foreign table
in the current database. The table will be owned by the user issuing the
command.
</P
><P
> If a schema name is given (for example, <TT
CLASS="LITERAL"
>CREATE FOREIGN TABLE
myschema.mytable ...</TT
>) then the table is created in the specified
schema. Otherwise it is created in the current schema.
The name of the foreign table must be
distinct from the name of any other foreign table, table, sequence, index,
view, or materialized view in the same schema.
</P
><P
> <TT
CLASS="COMMAND"
>CREATE FOREIGN TABLE</TT
> also automatically creates a data
type that represents the composite type corresponding to one row of
the foreign table. Therefore, foreign tables cannot have the same
name as any existing data type in the same schema.
</P
><P
> To be able to create a foreign table, you must have <TT
CLASS="LITERAL"
>USAGE</TT
>
privilege on the foreign server, as well as <TT
CLASS="LITERAL"
>USAGE</TT
>
privilege on all column types used in the table.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN80180"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>IF NOT EXISTS</TT
></DT
><DD
><P
> Do not throw an error if a relation with the same name already exists.
A notice is issued in this case. Note that there is no guarantee that
the existing relation is anything like the one that would have been
created.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
></DT
><DD
><P
> The name (optionally schema-qualified) of the table to be created.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
></DT
><DD
><P
> The name of a column to be created in the new table.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>data_type</I
></TT
></DT
><DD
><P
> The data type of the column. This can include array
specifiers. For more information on the data types supported by
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, refer to <A
HREF="datatype.html"
>Chapter 8</A
>.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>COLLATE <TT
CLASS="REPLACEABLE"
><I
>collation</I
></TT
></TT
></DT
><DD
><P
> The <TT
CLASS="LITERAL"
>COLLATE</TT
> clause assigns a collation to
the column (which must be of a collatable data type).
If not specified, the column data type's default collation is used.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>INHERITS ( <TT
CLASS="REPLACEABLE"
><I
>parent_table</I
></TT
> [, ... ] )</TT
></DT
><DD
><P
> The optional <TT
CLASS="LITERAL"
>INHERITS</TT
> clause specifies a list of
tables from which the new foreign table automatically inherits
all columns. Parent tables can be plain tables or foreign tables.
See the similar form of
<A
HREF="sql-createtable.html"
>CREATE TABLE</A
> for more details.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>CONSTRAINT <TT
CLASS="REPLACEABLE"
><I
>constraint_name</I
></TT
></TT
></DT
><DD
><P
> An optional name for a column or table constraint. If the
constraint is violated, the constraint name is present in error messages,
so constraint names like <TT
CLASS="LITERAL"
>col must be positive</TT
> can be used
to communicate helpful constraint information to client applications.
(Double-quotes are needed to specify constraint names that contain spaces.)
If a constraint name is not specified, the system generates a name.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>NOT NULL</TT
></DT
><DD
><P
> The column is not allowed to contain null values.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>NULL</TT
></DT
><DD
><P
> The column is allowed to contain null values. This is the default.
</P
><P
> This clause is only provided for compatibility with
non-standard SQL databases. Its use is discouraged in new
applications.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>CHECK ( <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ) [ NO INHERIT ] </TT
></DT
><DD
><P
> The <TT
CLASS="LITERAL"
>CHECK</TT
> clause specifies an expression producing a
Boolean result which each row in the foreign table is expected
to satisfy; that is, the expression should produce TRUE or UNKNOWN,
never FALSE, for all rows in the foreign table.
A check constraint specified as a column constraint should
reference that column's value only, while an expression
appearing in a table constraint can reference multiple columns.
</P
><P
> Currently, <TT
CLASS="LITERAL"
>CHECK</TT
> expressions cannot contain
subqueries nor refer to variables other than columns of the
current row. The system column <TT
CLASS="LITERAL"
>tableoid</TT
>
may be referenced, but not any other system column.
</P
><P
> A constraint marked with <TT
CLASS="LITERAL"
>NO INHERIT</TT
> will not propagate to
child tables.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>DEFAULT
<TT
CLASS="REPLACEABLE"
><I
>default_expr</I
></TT
></TT
></DT
><DD
><P
> The <TT
CLASS="LITERAL"
>DEFAULT</TT
> clause assigns a default data value for
the column whose column definition it appears within. The value
is any variable-free expression (subqueries and cross-references
to other columns in the current table are not allowed). The
data type of the default expression must match the data type of the
column.
</P
><P
> The default expression will be used in any insert operation that
does not specify a value for the column. If there is no default
for a column, then the default is null.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>server_name</I
></TT
></DT
><DD
><P
> The name of an existing foreign server to use for the foreign table.
For details on defining a server, see <A
HREF="sql-createserver.html"
>CREATE SERVER</A
>.
</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
> Options to be associated with the new foreign table or one of its
columns.
The allowed option names and values are specific to each foreign
data wrapper and are validated using the foreign-data wrapper's
validator function. Duplicate option names are not allowed (although
it's OK for a table option and a column option to have the same name).
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN80271"
></A
><H2
>Notes</H2
><P
> Constraints on foreign tables (such as <TT
CLASS="LITERAL"
>CHECK</TT
>
or <TT
CLASS="LITERAL"
>NOT NULL</TT
> clauses) are not enforced by the
core <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> system, and most foreign data wrappers
do not attempt to enforce them either; that is, the constraint is
simply assumed to hold true. There would be little point in such
enforcement since it would only apply to rows inserted or updated via
the foreign table, and not to rows modified by other means, such as
directly on the remote server. Instead, a constraint attached to a
foreign table should represent a constraint that is being enforced by
the remote server.
</P
><P
> Some special-purpose foreign data wrappers might be the only access
mechanism for the data they access, and in that case it might be
appropriate for the foreign data wrapper itself to perform constraint
enforcement. But you should not assume that a wrapper does that
unless its documentation says so.
</P
><P
> Although <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> does not attempt to enforce
constraints on foreign tables, it does assume that they are correct
for purposes of query optimization. If there are rows visible in the
foreign table that do not satisfy a declared constraint, queries on
the table might produce incorrect answers. It is the user's
responsibility to ensure that the constraint definition matches
reality.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATEFOREIGNTABLE-EXAMPLES"
></A
><H2
>Examples</H2
><P
> Create foreign table <TT
CLASS="STRUCTNAME"
>films</TT
>, which will be accessed through
the server <TT
CLASS="STRUCTNAME"
>film_server</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FOREIGN TABLE films (
code char(5) NOT NULL,
title varchar(40) NOT NULL,
did integer NOT NULL,
date_prod date,
kind varchar(10),
len interval hour to minute
)
SERVER film_server;</PRE
><P></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATEFOREIGNTABLE-COMPATIBILITY"
></A
><H2
>Compatibility</H2
><P
> The <TT
CLASS="COMMAND"
>CREATE FOREIGN TABLE</TT
> command largely conforms to the
<ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> standard; however, much as with
<A
HREF="sql-createtable.html"
><TT
CLASS="COMMAND"
>CREATE TABLE</TT
></A
>,
<TT
CLASS="LITERAL"
>NULL</TT
> constraints and zero-column foreign tables are permitted.
The ability to specify column default values is also
a <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extension. Table inheritance, in the form
defined by <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, is nonstandard.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN80296"
></A
><H2
>See Also</H2
><A
HREF="sql-alterforeigntable.html"
>ALTER FOREIGN TABLE</A
>, <A
HREF="sql-dropforeigntable.html"
>DROP FOREIGN TABLE</A
>, <A
HREF="sql-createtable.html"
>CREATE TABLE</A
>, <A
HREF="sql-createserver.html"
>CREATE SERVER</A
>, <A
HREF="sql-importforeignschema.html"
>IMPORT FOREIGN SCHEMA</A
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