Document new trigger-related forms of ALTER FOREIGN TABLE.

Oversight in commit 7cbe57c.
Back-patch to 9.4, where that commit first appeared.  In passing,
release-note the FDW API postcondition change from the same commit.

Author: nmisch

doc/src/sgml/ref/alter_foreign_table.sgml

@@ -42,6 +42,10 @@ ALTER FOREIGN TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceab
     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> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column_name</replaceable> OPTIONS ( [ ADD | SET | DROP ] <replaceable class="PARAMETER">option</replaceable> ['<replaceable class="PARAMETER">value</replaceable>'] [, ... ])
+    DISABLE TRIGGER [ <replaceable class="PARAMETER">trigger_name</replaceable> | ALL | USER ]
+    ENABLE TRIGGER [ <replaceable class="PARAMETER">trigger_name</replaceable> | ALL | USER ]
+    ENABLE REPLICA TRIGGER <replaceable class="PARAMETER">trigger_name</replaceable>
+    ENABLE ALWAYS TRIGGER <replaceable class="PARAMETER">trigger_name</replaceable>
     OWNER TO <replaceable class="PARAMETER">new_owner</replaceable>
     OPTIONS ( [ ADD | SET | DROP ] <replaceable class="PARAMETER">option</replaceable> ['<replaceable class="PARAMETER">value</replaceable>'] [, ... ])
 </synopsis>
@@ -148,6 +152,17 @@ ALTER FOREIGN TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceab
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>DISABLE</literal>/<literal>ENABLE [ REPLICA | ALWAYS ] TRIGGER</literal></term>
+    <listitem>
+     <para>
+      These forms configure the firing of trigger(s) belonging to the foreign
+      table.  See the similar form of <xref linkend="sql-altertable"> for more
+      details.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>OWNER</literal></term>
     <listitem>
@@ -289,6 +304,37 @@ ALTER FOREIGN TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceab
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><replaceable class="PARAMETER">trigger_name</replaceable></term>
+      <listitem>
+       <para>
+        Name of a single trigger to disable or enable.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
+      <term><literal>ALL</literal></term>
+      <listitem>
+       <para>
+        Disable or enable all triggers belonging to the foreign table.  (This
+        requires superuser privilege if any of the triggers are internally
+        generated triggers.  The core system does not add such triggers to
+        foreign tables, but add-on code could do so.)
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
+      <term><literal>USER</literal></term>
+      <listitem>
+       <para>
+        Disable or enable all triggers belonging to the foreign table except
+        for internally generated triggers.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><replaceable class="PARAMETER">new_owner</replaceable></term>
       <listitem>

doc/src/sgml/release-9.4.sgml

@@ -191,6 +191,18 @@
      </para>
     </listitem>
 
+    <listitem>
+     <para>
+      Writable foreign data wrappers must return all columns when the foreign
+      table has an <literal>AFTER ROW</> trigger (Noah Misch)
+     </para>
+
+     <para>
+      Previously, foreign tables never had triggers, and
+      the <literal>RETURNING</> clause alone dictated the columns required.
+     </para>
+    </listitem>
+
     <listitem>
      <para>
       Rename <link linkend="SQL-EXPLAIN"><command>EXPLAIN