Fix a couple of unlogged tables goofs.

"SELECT ... INTO UNLOGGED tabname" works, but wasn't documented; CREATE
UNLOGGED SEQUENCE and CREATE UNLOGGED VIEW failed an assertion, instead
of throwing a sensible error.

Latter issue reported by Itagaki Takahiro; patch review by Tom Lane.

doc/src/sgml/ref/select_into.sgml

@@ -24,7 +24,7 @@ PostgreSQL documentation
 [ WITH [ RECURSIVE ] <replaceable class="parameter">with_query</replaceable> [, ...] ]
 SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replaceable> [, ...] ) ] ]
     * | <replaceable class="parameter">expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</replaceable> ] [, ...]
-    INTO [ TEMPORARY | TEMP ] [ TABLE ] <replaceable class="parameter">new_table</replaceable>
+    INTO [ TEMPORARY | TEMP | UNLOGGED ] [ TABLE ] <replaceable class="parameter">new_table</replaceable>
     [ FROM <replaceable class="parameter">from_item</replaceable> [, ...] ]
     [ WHERE <replaceable class="parameter">condition</replaceable> ]
     [ GROUP BY <replaceable class="parameter">expression</replaceable> [, ...] ]
@@ -65,6 +65,16 @@ SELECT [ ALL | DISTINCT [ ON ( <replaceable class="parameter">expression</replac
    </listitem>
   </varlistentry>
 
+  <varlistentry>
+   <term><literal>UNLOGGED</literal></term>
+   <listitem>
+    <para>
+     If specified, the table is created as an unlogged table.  Refer
+     to <xref linkend="sql-createtable"> for details.
+    </para>
+   </listitem>
+  </varlistentry>
+
    <varlistentry>
     <term><replaceable class="PARAMETER">new_table</replaceable></term>
     <listitem>

src/backend/commands/sequence.c

@@ -119,6 +119,12 @@ DefineSequence(CreateSeqStmt *seq)
 	int			i;
 	NameData	name;
 
+	/* Unlogged sequences are not implemented -- not clear if useful. */
+	if (seq->sequence->relpersistence == RELPERSISTENCE_UNLOGGED)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("unlogged sequences are not supported")));
+
 	/* Check and set all option values */
 	init_params(seq->options, true, &new, &owned_by);
 

src/backend/commands/view.c

@@ -465,6 +465,12 @@ DefineView(ViewStmt *stmt, const char *queryString)
 						view->relname)));
 	}
 
+	/* Unlogged views are not sensible. */
+	if (view->relpersistence == RELPERSISTENCE_UNLOGGED)
+		ereport(ERROR,
+				(errcode(ERRCODE_SYNTAX_ERROR),
+				 errmsg("views cannot be unlogged because they do not have storage")));
+
 	/*
 	 * Create the view relation
 	 *