Fix estimate_expression_value to constant-fold SQLValueFunction nodes.

Oversight in my commit 0bb51aa96.  Noted while poking at a recent
bug report --- HEAD's estimates for a query using CURRENT_DATE
were unexpectedly much worse than 9.6's.

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 9598f28bab31f5a57b83f9180db9cbb9a7194a90..9af29dd5b12468fbd9e72737698fa74fe1d5c18a 100644 (file)
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -3346,6 +3346,23 @@ eval_const_expressions_mutator(Node *node,
                                newcoalesce->location = coalesceexpr->location;
                                return (Node *) newcoalesce;
                        }
+               case T_SQLValueFunction:
+                       {
+                               /*
+                                * All variants of SQLValueFunction are stable, so if we are
+                                * estimating the expression's value, we should evaluate the
+                                * current function value.  Otherwise just copy.
+                                */
+                               SQLValueFunction *svf = (SQLValueFunction *) node;
+
+                               if (context->estimate)
+                                       return (Node *) evaluate_expr((Expr *) svf,
+                                                                                                 svf->type,
+                                                                                                 svf->typmod,
+                                                                                                 InvalidOid);
+                               else
+                                       return copyObject((Node *) svf);
+                       }
                case T_FieldSelect:
                        {
                                /*