Add infrastructure to support EphemeralNamedRelation references.

A QueryEnvironment concept is added, which allows new types of
objects to be passed into queries from parsing on through
execution.  At this point, the only thing implemented is a
collection of EphemeralNamedRelation objects -- relations which
can be referenced by name in queries, but do not exist in the
catalogs.  The only type of ENR implemented is NamedTuplestore, but
provision is made to add more types fairly easily.

An ENR can carry its own TupleDesc or reference a relation in the
catalogs by relid.

Although these features can be used without SPI, convenience
functions are added to SPI so that ENRs can easily be used by code
run through SPI.

The initial use of all this is going to be transition tables in
AFTER triggers, but that will be added to each PL as a separate
commit.

An incidental effect of this patch is to produce a more informative
error message if an attempt is made to modify the contents of a CTE
from a referencing DML statement.  No tests previously covered that
possibility, so one is added.

Kevin Grittner and Thomas Munro
Reviewed by Heikki Linnakangas, David Fetter, and Thomas Munro
with valuable comments and suggestions from many others

1 files changed, 49 insertions, 10 deletions

diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index 4f391d2d411..e268a127d13 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -59,9 +59,12 @@ static Node *transformJoinUsingClause(ParseState *pstate,
 						 List *leftVars, List *rightVars);
 static Node *transformJoinOnClause(ParseState *pstate, JoinExpr *j,
 					  List *namespace);
+static RangeTblEntry *getRTEForSpecialRelationTypes(ParseState *pstate,
+						RangeVar *rv);
 static RangeTblEntry *transformTableEntry(ParseState *pstate, RangeVar *r);
 static RangeTblEntry *transformCTEReference(ParseState *pstate, RangeVar *r,
 					  CommonTableExpr *cte, Index levelsup);
+static RangeTblEntry *transformENRReference(ParseState *pstate, RangeVar *r);
 static RangeTblEntry *transformRangeSubselect(ParseState *pstate,
 						RangeSubselect *r);
 static RangeTblEntry *transformRangeFunction(ParseState *pstate,
@@ -181,6 +184,14 @@ setTargetTable(ParseState *pstate, RangeVar *relation,
 	RangeTblEntry *rte;
 	int			rtindex;
 
+	/* So far special relations are immutable; so they cannot be targets. */
+	rte = getRTEForSpecialRelationTypes(pstate, relation);
+	if (rte != NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("relation \"%s\" cannot be the target of a modifying statement",
+						relation->relname)));
+
 	/* Close old target; this could only happen for multi-action rules */
 	if (pstate->p_target_relation != NULL)
 		heap_close(pstate->p_target_relation, NoLock);
@@ -435,6 +446,20 @@ transformCTEReference(ParseState *pstate, RangeVar *r,
 }
 
 /*
+ * transformENRReference --- transform a RangeVar that references an ephemeral
+ * named relation
+ */
+static RangeTblEntry *
+transformENRReference(ParseState *pstate, RangeVar *r)
+{
+	RangeTblEntry *rte;
+
+	rte = addRangeTableEntryForENR(pstate, r, true);
+
+	return rte;
+}
+
+/*
  * transformRangeSubselect --- transform a sub-SELECT appearing in FROM
  */
 static RangeTblEntry *
@@ -1021,6 +1046,24 @@ transformRangeTableSample(ParseState *pstate, RangeTableSample *rts)
 	return tablesample;
 }
 
+
+static RangeTblEntry *
+getRTEForSpecialRelationTypes(ParseState *pstate, RangeVar *rv)
+{
+
+	CommonTableExpr *cte;
+	Index		levelsup;
+	RangeTblEntry *rte = NULL;
+
+	cte = scanNameSpaceForCTE(pstate, rv->relname, &levelsup);
+	if (cte)
+		rte = transformCTEReference(pstate, rv, cte, levelsup);
+	if (!rte && scanNameSpaceForENR(pstate, rv->relname))
+		rte = transformENRReference(pstate, rv);
+
+	return rte;
+}
+
 /*
  * transformFromClauseItem -
  *	  Transform a FROM-clause item, adding any required entries to the
@@ -1055,18 +1098,14 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		RangeTblEntry *rte = NULL;
 		int			rtindex;
 
-		/* if it is an unqualified name, it might be a CTE reference */
+		/*
+		 * if it is an unqualified name, it might be a CTE or tuplestore
+		 * reference
+		 */
 		if (!rv->schemaname)
-		{
-			CommonTableExpr *cte;
-			Index		levelsup;
-
-			cte = scanNameSpaceForCTE(pstate, rv->relname, &levelsup);
-			if (cte)
-				rte = transformCTEReference(pstate, rv, cte, levelsup);
-		}
+			rte = getRTEForSpecialRelationTypes(pstate, rv);
 
-		/* if not found as a CTE, must be a table reference */
+		/* if not found above, must be a table reference */
 		if (!rte)
 			rte = transformTableEntry(pstate, rv);