Fix DEFAULT-handling in multi-row VALUES lists for updatable views.

INSERT ... VALUES for a single VALUES row is implemented differently
from a multi-row VALUES list, which causes inconsistent behaviour in
the way that DEFAULT items are handled. In particular, when inserting
into an auto-updatable view on top of a table with a column default, a
DEFAULT item in a single VALUES row gets correctly replaced with the
table column's default, but for a multi-row VALUES list it is replaced
with NULL.

Fix this by allowing rewriteValuesRTE() to leave DEFAULT items in the
VALUES list untouched if the target relation is an auto-updatable view
and has no column default, deferring DEFAULT-expansion until the query
against the base relation is rewritten. For all other types of target
relation, including tables and trigger- and rule-updatable views, we
must continue to replace DEFAULT items with NULL in the absence of a
column default.

This is somewhat complicated by the fact that if an auto-updatable
view has DO ALSO rules attached, the VALUES lists for the product
queries need to be handled differently from the original query, since
the product queries need to act like rule-updatable views whereas the
original query has auto-updatable view semantics.

Back-patch to all supported versions.

Reported by Roger Curley (bug #15623). Patch by Amit Langote and me.

Discussion: https://postgr.es/m/15623-5d67a46788ec8b7f@postgresql.org

src/backend/rewrite/rewriteHandler.c

@@ -73,8 +73,8 @@ static TargetEntry *process_matched_tle(TargetEntry *src_tle,
 					TargetEntry *prior_tle,
 					const char *attrName);
 static Node *get_assignment_input(Node *node);
-static void rewriteValuesRTE(RangeTblEntry *rte, Relation target_relation,
-				 List *attrnos);
+static bool rewriteValuesRTE(Query *parsetree, RangeTblEntry *rte,
+				 Relation target_relation, List *attrnos, bool force_nulls);
 static void markQueryForLocking(Query *qry, Node *jtnode,
 					LockClauseStrength strength, LockWaitPolicy waitPolicy,
 					bool pushedDown);
@@ -1219,29 +1219,102 @@ searchForDefault(RangeTblEntry *rte)
  * the appropriate default expressions.  The other aspects of targetlist
  * rewriting need be applied only to the query's targetlist proper.
  *
+ * For an auto-updatable view, each DEFAULT item in the VALUES list is
+ * replaced with the default from the view, if it has one.  Otherwise it is
+ * left untouched so that the underlying base relation's default can be
+ * applied instead (when we later recurse to here after rewriting the query
+ * to refer to the base relation instead of the view).
+ *
+ * For other types of relation, including rule- and trigger-updatable views,
+ * all DEFAULT items are replaced, and if the target relation doesn't have a
+ * default, the value is explicitly set to NULL.
+ *
+ * Additionally, if force_nulls is true, the target relation's defaults are
+ * ignored and all DEFAULT items in the VALUES list are explicitly set to
+ * NULL, regardless of the target relation's type.  This is used for the
+ * product queries generated by DO ALSO rules attached to an auto-updatable
+ * view, for which we will have already called this function with force_nulls
+ * false.  For these product queries, we must then force any remaining DEFAULT
+ * items to NULL to provide concrete values for the rule actions.
+ * Essentially, this is a mix of the 2 cases above --- the original query is
+ * an insert into an auto-updatable view, and the product queries are inserts
+ * into a rule-updatable view.
+ *
  * Note that we currently can't support subscripted or field assignment
  * in the multi-VALUES case.  The targetlist will contain simple Vars
  * referencing the VALUES RTE, and therefore process_matched_tle() will
  * reject any such attempt with "multiple assignments to same column".
+ *
+ * Returns true if all DEFAULT items were replaced, and false if some were
+ * left untouched.
  */
-static void
-rewriteValuesRTE(RangeTblEntry *rte, Relation target_relation, List *attrnos)
+static bool
+rewriteValuesRTE(Query *parsetree, RangeTblEntry *rte,
+				 Relation target_relation, List *attrnos, bool force_nulls)
 {
 	List	   *newValues;
 	ListCell   *lc;
+	bool		isAutoUpdatableView;
+	bool		allReplaced;
 
 	/*
 	 * Rebuilding all the lists is a pretty expensive proposition in a big
 	 * VALUES list, and it's a waste of time if there aren't any DEFAULT
 	 * placeholders.  So first scan to see if there are any.
+	 *
+	 * We skip this check if force_nulls is true, because we know that there
+	 * are DEFAULT items present in that case.
 	 */
-	if (!searchForDefault(rte))
-		return;					/* nothing to do */
+	if (!force_nulls && !searchForDefault(rte))
+		return true;			/* nothing to do */
 
 	/* Check list lengths (we can assume all the VALUES sublists are alike) */
 	Assert(list_length(attrnos) == list_length(linitial(rte->values_lists)));
 
+	/*
+	 * Check if the target relation is an auto-updatable view, in which case
+	 * unresolved defaults will be left untouched rather than being set to
+	 * NULL.  If force_nulls is true, we always set DEFAULT items to NULL, so
+	 * skip this check in that case --- it isn't an auto-updatable view.
+	 */
+	isAutoUpdatableView = false;
+	if (!force_nulls &&
+		target_relation->rd_rel->relkind == RELKIND_VIEW &&
+		!view_has_instead_trigger(target_relation, CMD_INSERT))
+	{
+		List	   *locks;
+		bool		hasUpdate;
+		bool		found;
+		ListCell   *l;
+
+		/* Look for an unconditional DO INSTEAD rule */
+		locks = matchLocks(CMD_INSERT, target_relation->rd_rules,
+						   parsetree->resultRelation, parsetree, &hasUpdate);
+
+		found = false;
+		foreach(l, locks)
+		{
+			RewriteRule *rule_lock = (RewriteRule *) lfirst(l);
+
+			if (rule_lock->isInstead &&
+				rule_lock->qual == NULL)
+			{
+				found = true;
+				break;
+			}
+		}
+
+		/*
+		 * If we didn't find an unconditional DO INSTEAD rule, assume that the
+		 * view is auto-updatable.  If it isn't, rewriteTargetView() will
+		 * throw an error.
+		 */
+		if (!found)
+			isAutoUpdatableView = true;
+	}
+
 	newValues = NIL;
+	allReplaced = true;
 	foreach(lc, rte->values_lists)
 	{
 		List	   *sublist = (List *) lfirst(lc);
@@ -1261,17 +1334,26 @@ rewriteValuesRTE(RangeTblEntry *rte, Relation target_relation, List *attrnos)
 
 				att_tup = TupleDescAttr(target_relation->rd_att, attrno - 1);
 
-				if (!att_tup->attisdropped)
+				if (!force_nulls && !att_tup->attisdropped)
 					new_expr = build_column_default(target_relation, attrno);
 				else
 					new_expr = NULL;	/* force a NULL if dropped */
 
 				/*
 				 * If there is no default (ie, default is effectively NULL),
-				 * we've got to explicitly set the column to NULL.
+				 * we've got to explicitly set the column to NULL, unless the
+				 * target relation is an auto-updatable view.
 				 */
 				if (!new_expr)
 				{
+					if (isAutoUpdatableView)
+					{
+						/* Leave the value untouched */
+						newList = lappend(newList, col);
+						allReplaced = false;
+						continue;
+					}
+
 					new_expr = (Node *) makeConst(att_tup->atttypid,
 												  -1,
 												  att_tup->attcollation,
@@ -1296,6 +1378,8 @@ rewriteValuesRTE(RangeTblEntry *rte, Relation target_relation, List *attrnos)
 		newValues = lappend(newValues, newList);
 	}
 	rte->values_lists = newValues;
+
+	return allReplaced;
 }
 
 
@@ -3383,6 +3467,9 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 		List	   *locks;
 		List	   *product_queries;
 		bool		hasUpdate = false;
+		List	   *attrnos = NIL;
+		int			values_rte_index = 0;
+		bool		defaults_remaining = false;
 
 		result_relation = parsetree->resultRelation;
 		Assert(result_relation != 0);
@@ -3416,14 +3503,15 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 												  parsetree->rtable);
 
 					if (rte->rtekind == RTE_VALUES)
+					{
 						values_rte = rte;
+						values_rte_index = rtr->rtindex;
+					}
 				}
 			}
 
 			if (values_rte)
 			{
-				List	   *attrnos;
-
 				/* Process the main targetlist ... */
 				parsetree->targetList = rewriteTargetListIU(parsetree->targetList,
 															parsetree->commandType,
@@ -3432,7 +3520,9 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 															parsetree->resultRelation,
 															&attrnos);
 				/* ... and the VALUES expression lists */
-				rewriteValuesRTE(values_rte, rt_entry_relation, attrnos);
+				if (!rewriteValuesRTE(parsetree, values_rte,
+									  rt_entry_relation, attrnos, false))
+					defaults_remaining = true;
 			}
 			else
 			{
@@ -3487,6 +3577,33 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 									&returning,
 									&qual_product);
 
+		/*
+		 * If we have a VALUES RTE with any remaining untouched DEFAULT items,
+		 * and we got any product queries, finalize the VALUES RTE for each
+		 * product query (replacing the remaining DEFAULT items with NULLs).
+		 * We don't do this for the original query, because we know that it
+		 * must be an auto-insert on a view, and so should use the base
+		 * relation's defaults for any remaining DEFAULT items.
+		 */
+		if (defaults_remaining && product_queries != NIL)
+		{
+			ListCell   *n;
+
+			/*
+			 * Each product query has its own copy of the VALUES RTE at the
+			 * same index in the rangetable, so we must finalize each one.
+			 */
+			foreach(n, product_queries)
+			{
+				Query	   *pt = (Query *) lfirst(n);
+				RangeTblEntry *values_rte = rt_fetch(values_rte_index,
+													 pt->rtable);
+
+				rewriteValuesRTE(pt, values_rte, rt_entry_relation, attrnos,
+								 true); /* Force remaining defaults to NULL */
+			}
+		}
+
 		/*
 		 * If there were no INSTEAD rules, and the target relation is a view
 		 * without any INSTEAD OF triggers, see if the view can be

src/test/regress/expected/updatable_views.out

@@ -2774,3 +2774,156 @@ drop view rw_view1;
 drop table base_tbl;
 drop user regress_view_user1;
 drop user regress_view_user2;
+-- Test single- and multi-row inserts with table and view defaults.
+-- Table defaults should be used, unless overridden by view defaults.
+create table base_tab_def (a int, b text default 'Table default',
+                           c text default 'Table default', d text, e text);
+create view base_tab_def_view as select * from base_tab_def;
+alter view base_tab_def_view alter b set default 'View default';
+alter view base_tab_def_view alter d set default 'View default';
+insert into base_tab_def values (1);
+insert into base_tab_def values (2), (3);
+insert into base_tab_def values (4, default, default, default, default);
+insert into base_tab_def values (5, default, default, default, default),
+                                (6, default, default, default, default);
+insert into base_tab_def_view values (11);
+insert into base_tab_def_view values (12), (13);
+insert into base_tab_def_view values (14, default, default, default, default);
+insert into base_tab_def_view values (15, default, default, default, default),
+                                     (16, default, default, default, default);
+select * from base_tab_def order by a;
+ a  |       b       |       c       |      d       | e 
+----+---------------+---------------+--------------+---
+  1 | Table default | Table default |              | 
+  2 | Table default | Table default |              | 
+  3 | Table default | Table default |              | 
+  4 | Table default | Table default |              | 
+  5 | Table default | Table default |              | 
+  6 | Table default | Table default |              | 
+ 11 | View default  | Table default | View default | 
+ 12 | View default  | Table default | View default | 
+ 13 | View default  | Table default | View default | 
+ 14 | View default  | Table default | View default | 
+ 15 | View default  | Table default | View default | 
+ 16 | View default  | Table default | View default | 
+(12 rows)
+
+-- Adding an INSTEAD OF trigger should cause NULLs to be inserted instead of
+-- table defaults, where there are no view defaults.
+create function base_tab_def_view_instrig_func() returns trigger
+as
+$$
+begin
+  insert into base_tab_def values (new.a, new.b, new.c, new.d, new.e);
+  return new;
+end;
+$$
+language plpgsql;
+create trigger base_tab_def_view_instrig instead of insert on base_tab_def_view
+  for each row execute function base_tab_def_view_instrig_func();
+truncate base_tab_def;
+insert into base_tab_def values (1);
+insert into base_tab_def values (2), (3);
+insert into base_tab_def values (4, default, default, default, default);
+insert into base_tab_def values (5, default, default, default, default),
+                                (6, default, default, default, default);
+insert into base_tab_def_view values (11);
+insert into base_tab_def_view values (12), (13);
+insert into base_tab_def_view values (14, default, default, default, default);
+insert into base_tab_def_view values (15, default, default, default, default),
+                                     (16, default, default, default, default);
+select * from base_tab_def order by a;
+ a  |       b       |       c       |      d       | e 
+----+---------------+---------------+--------------+---
+  1 | Table default | Table default |              | 
+  2 | Table default | Table default |              | 
+  3 | Table default | Table default |              | 
+  4 | Table default | Table default |              | 
+  5 | Table default | Table default |              | 
+  6 | Table default | Table default |              | 
+ 11 | View default  |               | View default | 
+ 12 | View default  |               | View default | 
+ 13 | View default  |               | View default | 
+ 14 | View default  |               | View default | 
+ 15 | View default  |               | View default | 
+ 16 | View default  |               | View default | 
+(12 rows)
+
+-- Using an unconditional DO INSTEAD rule should also cause NULLs to be
+-- inserted where there are no view defaults.
+drop trigger base_tab_def_view_instrig on base_tab_def_view;
+drop function base_tab_def_view_instrig_func;
+create rule base_tab_def_view_ins_rule as on insert to base_tab_def_view
+  do instead insert into base_tab_def values (new.a, new.b, new.c, new.d, new.e);
+truncate base_tab_def;
+insert into base_tab_def values (1);
+insert into base_tab_def values (2), (3);
+insert into base_tab_def values (4, default, default, default, default);
+insert into base_tab_def values (5, default, default, default, default),
+                                (6, default, default, default, default);
+insert into base_tab_def_view values (11);
+insert into base_tab_def_view values (12), (13);
+insert into base_tab_def_view values (14, default, default, default, default);
+insert into base_tab_def_view values (15, default, default, default, default),
+                                     (16, default, default, default, default);
+select * from base_tab_def order by a;
+ a  |       b       |       c       |      d       | e 
+----+---------------+---------------+--------------+---
+  1 | Table default | Table default |              | 
+  2 | Table default | Table default |              | 
+  3 | Table default | Table default |              | 
+  4 | Table default | Table default |              | 
+  5 | Table default | Table default |              | 
+  6 | Table default | Table default |              | 
+ 11 | View default  |               | View default | 
+ 12 | View default  |               | View default | 
+ 13 | View default  |               | View default | 
+ 14 | View default  |               | View default | 
+ 15 | View default  |               | View default | 
+ 16 | View default  |               | View default | 
+(12 rows)
+
+-- A DO ALSO rule should cause each row to be inserted twice. The first
+-- insert should behave the same as an auto-updatable view (using table
+-- defaults, unless overridden by view defaults). The second insert should
+-- behave the same as a rule-updatable view (inserting NULLs where there are
+-- no view defaults).
+drop rule base_tab_def_view_ins_rule on base_tab_def_view;
+create rule base_tab_def_view_ins_rule as on insert to base_tab_def_view
+  do also insert into base_tab_def values (new.a, new.b, new.c, new.d, new.e);
+truncate base_tab_def;
+insert into base_tab_def values (1);
+insert into base_tab_def values (2), (3);
+insert into base_tab_def values (4, default, default, default, default);
+insert into base_tab_def values (5, default, default, default, default),
+                                (6, default, default, default, default);
+insert into base_tab_def_view values (11);
+insert into base_tab_def_view values (12), (13);
+insert into base_tab_def_view values (14, default, default, default, default);
+insert into base_tab_def_view values (15, default, default, default, default),
+                                     (16, default, default, default, default);
+select * from base_tab_def order by a, c NULLS LAST;
+ a  |       b       |       c       |      d       | e 
+----+---------------+---------------+--------------+---
+  1 | Table default | Table default |              | 
+  2 | Table default | Table default |              | 
+  3 | Table default | Table default |              | 
+  4 | Table default | Table default |              | 
+  5 | Table default | Table default |              | 
+  6 | Table default | Table default |              | 
+ 11 | View default  | Table default | View default | 
+ 11 | View default  |               | View default | 
+ 12 | View default  | Table default | View default | 
+ 12 | View default  |               | View default | 
+ 13 | View default  | Table default | View default | 
+ 13 | View default  |               | View default | 
+ 14 | View default  | Table default | View default | 
+ 14 | View default  |               | View default | 
+ 15 | View default  | Table default | View default | 
+ 15 | View default  |               | View default | 
+ 16 | View default  | Table default | View default | 
+ 16 | View default  |               | View default | 
+(18 rows)
+
+drop view base_tab_def_view;
+drop table base_tab_def;

src/test/regress/sql/updatable_views.sql

@@ -1382,3 +1382,91 @@ drop view rw_view1;
 drop table base_tbl;
 drop user regress_view_user1;
 drop user regress_view_user2;
+
+-- Test single- and multi-row inserts with table and view defaults.
+-- Table defaults should be used, unless overridden by view defaults.
+create table base_tab_def (a int, b text default 'Table default',
+                           c text default 'Table default', d text, e text);
+create view base_tab_def_view as select * from base_tab_def;
+alter view base_tab_def_view alter b set default 'View default';
+alter view base_tab_def_view alter d set default 'View default';
+insert into base_tab_def values (1);
+insert into base_tab_def values (2), (3);
+insert into base_tab_def values (4, default, default, default, default);
+insert into base_tab_def values (5, default, default, default, default),
+                                (6, default, default, default, default);
+insert into base_tab_def_view values (11);
+insert into base_tab_def_view values (12), (13);
+insert into base_tab_def_view values (14, default, default, default, default);
+insert into base_tab_def_view values (15, default, default, default, default),
+                                     (16, default, default, default, default);
+select * from base_tab_def order by a;
+
+-- Adding an INSTEAD OF trigger should cause NULLs to be inserted instead of
+-- table defaults, where there are no view defaults.
+create function base_tab_def_view_instrig_func() returns trigger
+as
+$$
+begin
+  insert into base_tab_def values (new.a, new.b, new.c, new.d, new.e);
+  return new;
+end;
+$$
+language plpgsql;
+create trigger base_tab_def_view_instrig instead of insert on base_tab_def_view
+  for each row execute function base_tab_def_view_instrig_func();
+truncate base_tab_def;
+insert into base_tab_def values (1);
+insert into base_tab_def values (2), (3);
+insert into base_tab_def values (4, default, default, default, default);
+insert into base_tab_def values (5, default, default, default, default),
+                                (6, default, default, default, default);
+insert into base_tab_def_view values (11);
+insert into base_tab_def_view values (12), (13);
+insert into base_tab_def_view values (14, default, default, default, default);
+insert into base_tab_def_view values (15, default, default, default, default),
+                                     (16, default, default, default, default);
+select * from base_tab_def order by a;
+
+-- Using an unconditional DO INSTEAD rule should also cause NULLs to be
+-- inserted where there are no view defaults.
+drop trigger base_tab_def_view_instrig on base_tab_def_view;
+drop function base_tab_def_view_instrig_func;
+create rule base_tab_def_view_ins_rule as on insert to base_tab_def_view
+  do instead insert into base_tab_def values (new.a, new.b, new.c, new.d, new.e);
+truncate base_tab_def;
+insert into base_tab_def values (1);
+insert into base_tab_def values (2), (3);
+insert into base_tab_def values (4, default, default, default, default);
+insert into base_tab_def values (5, default, default, default, default),
+                                (6, default, default, default, default);
+insert into base_tab_def_view values (11);
+insert into base_tab_def_view values (12), (13);
+insert into base_tab_def_view values (14, default, default, default, default);
+insert into base_tab_def_view values (15, default, default, default, default),
+                                     (16, default, default, default, default);
+select * from base_tab_def order by a;
+
+-- A DO ALSO rule should cause each row to be inserted twice. The first
+-- insert should behave the same as an auto-updatable view (using table
+-- defaults, unless overridden by view defaults). The second insert should
+-- behave the same as a rule-updatable view (inserting NULLs where there are
+-- no view defaults).
+drop rule base_tab_def_view_ins_rule on base_tab_def_view;
+create rule base_tab_def_view_ins_rule as on insert to base_tab_def_view
+  do also insert into base_tab_def values (new.a, new.b, new.c, new.d, new.e);
+truncate base_tab_def;
+insert into base_tab_def values (1);
+insert into base_tab_def values (2), (3);
+insert into base_tab_def values (4, default, default, default, default);
+insert into base_tab_def values (5, default, default, default, default),
+                                (6, default, default, default, default);
+insert into base_tab_def_view values (11);
+insert into base_tab_def_view values (12), (13);
+insert into base_tab_def_view values (14, default, default, default, default);
+insert into base_tab_def_view values (15, default, default, default, default),
+                                     (16, default, default, default, default);
+select * from base_tab_def order by a, c NULLS LAST;
+
+drop view base_tab_def_view;
+drop table base_tab_def;