Hi,
I was looking at the CREATE FOREIGN TABLE documentation to see if IDENTITY
columns were supported, and according to the doc they're not: only GENERATED
ALWAYS AS ( expr ) STORED is supported.
However, a quick test shows that this is supported (same as serial datatype),
and apparently behaves as expected. Looking at the grammar, CreateStmt and
CreateForeignTableStmt actually share the same rule for the column definitions
(OptTableElementList) so the behavior seems expected. The parse analysis code
is also mostly shared between the two, with only a few stuff explicitly
forbidden for foreign tables (primary keys and such).
It looks like this is just an oversight in the documentation? If so, it seems
like the CREATE and ALTER FOREIGN TABLE pages needs to be updated. The ALTER
FOREIGN TABLE page is also at least lacking the SET / DROP EXPRESSION clauses.
I'm attaching an initial patch for the missing parts that I could spot after a
quick look.
diff --git a/doc/src/sgml/ref/alter_foreign_table.sgml
b/doc/src/sgml/ref/alter_foreign_table.sgml
index 3cb6f08fcf..1672f548ef 100644
--- a/doc/src/sgml/ref/alter_foreign_table.sgml
+++ b/doc/src/sgml/ref/alter_foreign_table.sgml
@@ -38,6 +38,11 @@ ALTER FOREIGN TABLE [ IF EXISTS ] <replaceable
class="parameter">name</replaceab
ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
SET DEFAULT <replaceable class="parameter">expression</replaceable>
ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
DROP DEFAULT
ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
{ SET | DROP } NOT NULL
+ ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
SET EXPRESSION AS ( <replaceable class="parameter">expression</replaceable> )
+ ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
DROP EXPRESSION [ IF EXISTS ]
+ ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ (
<replaceable>sequence_options</replaceable> ) ]
+ ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
{ SET GENERATED { ALWAYS | BY DEFAULT } | SET
<replaceable>sequence_option</replaceable> | RESTART [ [ WITH ] <replaceable
class="parameter">restart</replaceable> ] } [...]
+ ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
DROP IDENTITY [ IF EXISTS ]
ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
SET STATISTICS <replaceable class="parameter">integer</replaceable>
ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
SET ( <replaceable class="parameter">attribute_option</replaceable> =
<replaceable class="parameter">value</replaceable> [, ... ] )
ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable>
RESET ( <replaceable class="parameter">attribute_option</replaceable> [, ... ] )
diff --git a/doc/src/sgml/ref/create_foreign_table.sgml
b/doc/src/sgml/ref/create_foreign_table.sgml
index dc4b907599..9c6851f47d 100644
--- a/doc/src/sgml/ref/create_foreign_table.sgml
+++ b/doc/src/sgml/ref/create_foreign_table.sgml
@@ -48,6 +48,7 @@ CREATE FOREIGN TABLE [ IF NOT EXISTS ] <replaceable
class="parameter">table_name
CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO
INHERIT ] |
DEFAULT <replaceable>default_expr</replaceable> |
GENERATED ALWAYS AS ( <replaceable>generation_expr</replaceable> ) STORED }
+ GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ (
<replaceable>sequence_options</replaceable> ) ] |
<phrase>and <replaceable class="parameter">table_constraint</replaceable>
is:</phrase>
@@ -309,6 +310,52 @@ WITH ( MODULUS <replaceable
class="parameter">numeric_literal</replaceable>, REM
</listitem>
</varlistentry>
+ <varlistentry>
+ <term><literal>GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ (
<replaceable>sequence_options</replaceable> ) ]</literal></term>
+ <listitem>
+ <para>
+ This clause creates the column as an <firstterm>identity
+ column</firstterm>. It will have an implicit sequence attached to it
+ and the column in new rows will automatically have values from the
+ sequence assigned to it. (The computed value will be presented
+ to the foreign-data wrapper for storage and must be returned on
+ reading.)
+ Such a column is implicitly <literal>NOT NULL</literal>.
+ </para>
+
+ <para>
+ The clauses <literal>ALWAYS</literal> and <literal>BY DEFAULT</literal>
+ determine how explicitly user-specified values are handled in
+ <command>INSERT</command> and <command>UPDATE</command> commands.
+ </para>
+
+ <para>
+ In an <command>INSERT</command> command, if <literal>ALWAYS</literal> is
+ selected, a user-specified value is only accepted if the
+ <command>INSERT</command> statement specifies <literal>OVERRIDING SYSTEM
+ VALUE</literal>. If <literal>BY DEFAULT</literal> is selected, then the
+ user-specified value takes precedence. See <xref linkend="sql-insert"/>
+ for details. (In the <command>COPY</command> command, user-specified
+ values are always used regardless of this setting.)
+ </para>
+
+ <para>
+ In an <command>UPDATE</command> command, if <literal>ALWAYS</literal> is
+ selected, any update of the column to any value other than
+ <literal>DEFAULT</literal> will be rejected. If <literal>BY
+ DEFAULT</literal> is selected, the column can be updated normally.
+ (There is no <literal>OVERRIDING</literal> clause for the
+ <command>UPDATE</command> command.)
+ </para>
+
+ <para>
+ The optional <replaceable>sequence_options</replaceable> clause can be
+ used to override the options of the sequence.
+ See <xref linkend="sql-createsequence"/> for details.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry>
<term><literal>OPTIONS ( <replaceable
class="parameter">option</replaceable> '<replaceable
class="parameter">value</replaceable>' [, ...] )</literal></term>
<listitem>
