Add a materialized view relations.

A materialized view has a rule just like a view and a heap and
other physical properties like a table.  The rule is only used to
populate the table, references in queries refer to the
materialized data.

This is a minimal implementation, but should still be useful in
many cases.  Currently data is only populated "on demand" by the
CREATE MATERIALIZED VIEW and REFRESH MATERIALIZED VIEW statements.
It is expected that future releases will add incremental updates
with various timings, and that a more refined concept of defining
what is "fresh" data will be developed.  At some point it may even
be possible to have queries use a materialized in place of
references to underlying tables, but that requires the other
above-mentioned features to be working first.

Much of the documentation work by Robert Haas.
Review by Noah Misch, Thom Brown, Robert Haas, Marko Tiikkaja
Security review by KaiGai Kohei, with a decision on how best to
implement sepgsql still pending.

src/include/nodes/parsenodes.h

@@ -713,6 +713,7 @@ typedef struct RangeTblEntry
 	 */
 	Oid			relid;			/* OID of the relation */
 	char		relkind;		/* relation kind (see pg_class.relkind) */
+	bool		isResultRel;	/* used in target of SELECT INTO or similar */
 
 	/*
 	 * Fields valid for a subquery RTE (else NULL):
@@ -1135,6 +1136,7 @@ typedef enum ObjectType
 	OBJECT_INDEX,
 	OBJECT_LANGUAGE,
 	OBJECT_LARGEOBJECT,
+	OBJECT_MATVIEW,
 	OBJECT_OPCLASS,
 	OBJECT_OPERATOR,
 	OBJECT_OPFAMILY,
@@ -2447,6 +2449,8 @@ typedef struct ExplainStmt
  * A query written as CREATE TABLE AS will produce this node type natively.
  * A query written as SELECT ... INTO will be transformed to this form during
  * parse analysis.
+ * A query written as CREATE MATERIALIZED view will produce this node type,
+ * during parse analysis, since it needs all the same data.
  *
  * The "query" field is handled similarly to EXPLAIN, though note that it
  * can be a SELECT or an EXECUTE, but not other DML statements.
@@ -2457,9 +2461,21 @@ typedef struct CreateTableAsStmt
 	NodeTag		type;
 	Node	   *query;			/* the query (see comments above) */
 	IntoClause *into;			/* destination table */
+	ObjectType	relkind;		/* type of object */
 	bool		is_select_into; /* it was written as SELECT INTO */
 } CreateTableAsStmt;
 
+/* ----------------------
+ *		REFRESH MATERIALIZED VIEW Statement
+ * ----------------------
+ */
+typedef struct RefreshMatViewStmt
+{
+	NodeTag		type;
+	bool		skipData;		/* true for WITH NO DATA */
+	RangeVar   *relation;		/* relation to insert into */
+} RefreshMatViewStmt;
+
 /* ----------------------
  * Checkpoint Statement
  * ----------------------
@@ -2517,7 +2533,7 @@ typedef struct ConstraintsSetStmt
 typedef struct ReindexStmt
 {
 	NodeTag		type;
-	ObjectType	kind;			/* OBJECT_INDEX, OBJECT_TABLE, OBJECT_DATABASE */
+	ObjectType	kind;			/* OBJECT_INDEX, OBJECT_TABLE, etc. */
 	RangeVar   *relation;		/* Table or index to reindex */
 	const char *name;			/* name of database to reindex */
 	bool		do_system;		/* include system tables in database case */