Extend whole-row Var evaluation to cope with the case that the sub-plan

generating the tuples has resjunk output columns.  This is not possible for
simple table scans but can happen when evaluating a whole-row Var for a view.
Per example from Patryk Kordylewski.  The problem exists back to 8.0 but
I'm not going to risk back-patching further than 8.2 because of the many
changes in this area.

diff --git a/src/backend/executor/execQual.c b/src/backend/executor/execQual.c
index 69d28e78a4b8336f8ec0f11b66a62b50d844d6a4..85c3be3e8dd93c43ed2fd69a947bf9af2b7b4cb4 100644 (file)
--- a/src/backend/executor/execQual.c
+++ b/src/backend/executor/execQual.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.220 2007/06/11 22:22:40 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.221 2007/08/31 18:33:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -68,6 +68,8 @@ static Datum ExecEvalScalarVar(ExprState *exprstate, ExprContext *econtext,
            bool *isNull, ExprDoneCond *isDone);
 static Datum ExecEvalWholeRowVar(ExprState *exprstate, ExprContext *econtext,
                    bool *isNull, ExprDoneCond *isDone);
+static Datum ExecEvalWholeRowSlow(ExprState *exprstate, ExprContext *econtext,
+                   bool *isNull, ExprDoneCond *isDone);
 static Datum ExecEvalConst(ExprState *exprstate, ExprContext *econtext,
              bool *isNull, ExprDoneCond *isDone);
 static Datum ExecEvalParam(ExprState *exprstate, ExprContext *econtext,
@@ -438,7 +440,8 @@ ExecEvalAggref(AggrefExprState *aggref, ExprContext *econtext,
  *
  * Note: ExecEvalVar is executed only the first time through in a given plan;
  * it changes the ExprState's function pointer to pass control directly to
- * ExecEvalScalarVar or ExecEvalWholeRowVar after making one-time checks.
+ * ExecEvalScalarVar, ExecEvalWholeRowVar, or ExecEvalWholeRowSlow after
+ * making one-time checks.
  * ----------------------------------------------------------------
  */
 static Datum
@@ -544,6 +547,7 @@ ExecEvalVar(ExprState *exprstate, ExprContext *econtext,
         * the actual tuple type is compatible with it.
         */
        TupleDesc   slot_tupdesc = slot->tts_tupleDescriptor;
+       bool        needslow = false;
 
        if (variable->vartype == RECORDOID)
        {
@@ -561,16 +565,26 @@ ExecEvalVar(ExprState *exprstate, ExprContext *econtext,
             * Also, we can ignore type mismatch on columns that are dropped
             * in the destination type, so long as the physical storage
             * matches.  This is helpful in some cases involving out-of-date
-            * cached plans.
+            * cached plans.  Also, we have to allow the case that the slot
+            * has more columns than the Var's type, because we might be
+            * looking at the output of a subplan that includes resjunk
+            * columns.  (XXX it would be nice to verify that the extra
+            * columns are all marked resjunk, but we haven't got access to
+            * the subplan targetlist here...)  Resjunk columns should always
+            * be at the end of a targetlist, so it's sufficient to ignore
+            * them here; but we need to use ExecEvalWholeRowSlow to get
+            * rid of them in the eventual output tuples.
             */
            var_tupdesc = lookup_rowtype_tupdesc(variable->vartype, -1);
 
-           if (var_tupdesc->natts != slot_tupdesc->natts)
+           if (var_tupdesc->natts > slot_tupdesc->natts)
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                         errmsg("table row type and query-specified row type do not match"),
                         errdetail("Table row contains %d attributes, but query expects %d.",
                                   slot_tupdesc->natts, var_tupdesc->natts)));
+           else if (var_tupdesc->natts < slot_tupdesc->natts)
+               needslow = true;
 
            for (i = 0; i < var_tupdesc->natts; i++)
            {
@@ -601,7 +615,10 @@ ExecEvalVar(ExprState *exprstate, ExprContext *econtext,
        }
 
        /* Skip the checking on future executions of node */
-       exprstate->evalfunc = ExecEvalWholeRowVar;
+       if (needslow)
+           exprstate->evalfunc = ExecEvalWholeRowSlow;
+       else
+           exprstate->evalfunc = ExecEvalWholeRowVar;
 
        /* Fetch the value */
        return ExecEvalWholeRowVar(exprstate, econtext, isNull, isDone);
@@ -698,6 +715,60 @@ ExecEvalWholeRowVar(ExprState *exprstate, ExprContext *econtext,
    return PointerGetDatum(dtuple);
 }
 
+/* ----------------------------------------------------------------
+ *     ExecEvalWholeRowSlow
+ *
+ *     Returns a Datum for a whole-row variable, in the "slow" case where
+ *     we can't just copy the subplan's output.
+ * ----------------------------------------------------------------
+ */
+static Datum
+ExecEvalWholeRowSlow(ExprState *exprstate, ExprContext *econtext,
+                    bool *isNull, ExprDoneCond *isDone)
+{
+   Var        *variable = (Var *) exprstate->expr;
+   TupleTableSlot *slot = econtext->ecxt_scantuple;
+   HeapTuple   tuple;
+   TupleDesc   var_tupdesc;
+   HeapTupleHeader dtuple;
+
+   if (isDone)
+       *isDone = ExprSingleResult;
+   *isNull = false;
+
+   /*
+    * Currently, the only case handled here is stripping of trailing
+    * resjunk fields, which we do in a slightly chintzy way by just
+    * adjusting the tuple's natts header field.  Possibly there will someday
+    * be a need for more-extensive rearrangements, in which case it'd
+    * be worth disassembling and reassembling the tuple (perhaps use a
+    * JunkFilter for that?)
+    */
+   Assert(variable->vartype != RECORDOID);
+   var_tupdesc = lookup_rowtype_tupdesc(variable->vartype, -1);
+
+   tuple = ExecFetchSlotTuple(slot);
+
+   /*
+    * We have to make a copy of the tuple so we can safely insert the Datum
+    * overhead fields, which are not set in on-disk tuples; not to mention
+    * fooling with its natts field.
+    */
+   dtuple = (HeapTupleHeader) palloc(tuple->t_len);
+   memcpy((char *) dtuple, (char *) tuple->t_data, tuple->t_len);
+
+   HeapTupleHeaderSetDatumLength(dtuple, tuple->t_len);
+   HeapTupleHeaderSetTypeId(dtuple, variable->vartype);
+   HeapTupleHeaderSetTypMod(dtuple, variable->vartypmod);
+
+   Assert(HeapTupleHeaderGetNatts(dtuple) >= var_tupdesc->natts);
+   HeapTupleHeaderSetNatts(dtuple, var_tupdesc->natts);
+
+   ReleaseTupleDesc(var_tupdesc);
+
+   return PointerGetDatum(dtuple);
+}
+
 /* ----------------------------------------------------------------
  *     ExecEvalConst
  *