Implement SQL-standard WITH clauses, including WITH RECURSIVE.

There are some unimplemented aspects: recursive queries must use UNION ALL
(should allow UNION too), and we don't have SEARCH or CYCLE clauses.
These might or might not get done for 8.4, but even without them it's a
pretty useful feature.

There are also a couple of small loose ends and definitional quibbles,
which I'll send a memo about to pgsql-hackers shortly.  But let's land
the patch now so we can get on with other development.

Yoshiyuki Asaba, with lots of help from Tatsuo Ishii and Tom Lane

1 files changed, 54 insertions, 4 deletions

diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index 2f547f29be6..dbf17759617 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_clause.c,v 1.179 2008/09/01 20:42:44 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_clause.c,v 1.180 2008/10/04 21:56:54 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -54,6 +54,8 @@ static Node *transformJoinOnClause(ParseState *pstate, JoinExpr *j,
 					  List *relnamespace,
 					  Relids containedRels);
 static RangeTblEntry *transformTableEntry(ParseState *pstate, RangeVar *r);
+static RangeTblEntry *transformCTEReference(ParseState *pstate, RangeVar *r,
+					  CommonTableExpr *cte, Index levelsup);
 static RangeTblEntry *transformRangeSubselect(ParseState *pstate,
 						RangeSubselect *r);
 static RangeTblEntry *transformRangeFunction(ParseState *pstate,
@@ -422,6 +424,20 @@ transformTableEntry(ParseState *pstate, RangeVar *r)
 	return rte;
 }
 
+/*
+ * transformCTEReference --- transform a RangeVar that references a common
+ * table expression (ie, a sub-SELECT defined in a WITH clause)
+ */
+static RangeTblEntry *
+transformCTEReference(ParseState *pstate, RangeVar *r,
+					  CommonTableExpr *cte, Index levelsup)
+{
+	RangeTblEntry *rte;
+
+	rte = addRangeTableEntryForCTE(pstate, cte, levelsup, r->alias, true);
+
+	return rte;
+}
 
 /*
  * transformRangeSubselect --- transform a sub-SELECT appearing in FROM
@@ -609,12 +625,46 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 {
 	if (IsA(n, RangeVar))
 	{
-		/* Plain relation reference */
+		/* Plain relation reference, or perhaps a CTE reference */
+		RangeVar *rv = (RangeVar *) n;
 		RangeTblRef *rtr;
-		RangeTblEntry *rte;
+		RangeTblEntry *rte = NULL;
 		int			rtindex;
 
-		rte = transformTableEntry(pstate, (RangeVar *) n);
+		/*
+		 * If it is an unqualified name, it might be a reference to some
+		 * CTE visible in this or a parent query.
+		 */
+		if (!rv->schemaname)
+		{
+			ParseState *ps;
+			Index	levelsup;
+
+			for (ps = pstate, levelsup = 0;
+				 ps != NULL;
+				 ps = ps->parentParseState, levelsup++)
+			{
+				ListCell *lc;
+
+				foreach(lc, ps->p_ctenamespace)
+				{
+					CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);
+
+					if (strcmp(rv->relname, cte->ctename) == 0)
+					{
+						rte = transformCTEReference(pstate, rv, cte, levelsup);
+						break;
+					}
+				}
+				if (rte)
+					break;
+			}
+		}
+
+		/* if not found as a CTE, must be a table reference */
+		if (!rte)
+			rte = transformTableEntry(pstate, rv);
+
 		/* assume new rte is at end */
 		rtindex = list_length(pstate->p_rtable);
 		Assert(rte == rt_fetch(rtindex, pstate->p_rtable));