WITH CHECK OPTION support for auto-updatable VIEWs

For simple views which are automatically updatable, this patch allows
the user to specify what level of checking should be done on records
being inserted or updated.  For 'LOCAL CHECK', new tuples are validated
against the conditionals of the view they are being inserted into, while
for 'CASCADED CHECK' the new tuples are validated against the
conditionals for all views involved (from the top down).

This option is part of the SQL specification.

Dean Rasheed, reviewed by Pavel Stehule

src/include/nodes/parsenodes.h

@@ -128,6 +128,8 @@ typedef struct Query
 
 	List	   *targetList;		/* target list (of TargetEntry) */
 
+	List	   *withCheckOptions; /* a list of WithCheckOption's */
+
 	List	   *returningList;	/* return-values list (of TargetEntry) */
 
 	List	   *groupClause;	/* a list of SortGroupClause's */
@@ -783,6 +785,19 @@ typedef struct RangeTblEntry
 	Bitmapset  *modifiedCols;	/* columns needing INSERT/UPDATE permission */
 } RangeTblEntry;
 
+/*
+ * WithCheckOption -
+ *		representation of WITH CHECK OPTION checks to be applied to new tuples
+ *		when inserting/updating an auto-updatable view.
+ */
+typedef struct WithCheckOption
+{
+	NodeTag		type;
+	char	   *viewname;	/* name of view that specified the WCO */
+	Node	   *qual;		/* constraint qual to check */
+	bool		cascaded;	/* true = WITH CASCADED CHECK OPTION */
+} WithCheckOption;
+
 /*
  * SortGroupClause -
  *		representation of ORDER BY, GROUP BY, PARTITION BY,
@@ -2333,6 +2348,13 @@ typedef struct AlterEnumStmt
  *		Create View Statement
  * ----------------------
  */
+typedef enum ViewCheckOption
+{
+	NO_CHECK_OPTION,
+	LOCAL_CHECK_OPTION,
+	CASCADED_CHECK_OPTION
+} ViewCheckOption;
+
 typedef struct ViewStmt
 {
 	NodeTag		type;
@@ -2341,6 +2363,7 @@ typedef struct ViewStmt
 	Node	   *query;			/* the SELECT query */
 	bool		replace;		/* replace an existing view? */
 	List	   *options;		/* options from WITH clause */
+	ViewCheckOption	withCheckOption; /* WITH CHECK OPTION */
 } ViewStmt;
 
 /* ----------------------