From a371ca5f3bf7a9d7602aa5531a90e64c62111135 Mon Sep 17 00:00:00 2001
From: Shigeru Hanada <hanada@metrosystems.co.jp>
Date: Thu, 24 Feb 2011 11:45:38 +0900
Subject: [PATCH] Gather used column from baserestrictinfo and reltargetlist of
 RelOptInfo.

---
 contrib/postgresql_fdw/postgresql_fdw.c | 41 ++++++++++++++++++++++---
 1 file changed, 36 insertions(+), 5 deletions(-)

diff --git a/contrib/postgresql_fdw/postgresql_fdw.c b/contrib/postgresql_fdw/postgresql_fdw.c
index 70e7500b06..940ff1f8d0 100644
--- a/contrib/postgresql_fdw/postgresql_fdw.c
+++ b/contrib/postgresql_fdw/postgresql_fdw.c
@@ -27,6 +27,7 @@
 #include "optimizer/clauses.h"
 #include "optimizer/cost.h"
 #include "optimizer/plancat.h"
+#include "optimizer/var.h"
 #include "parser/parsetree.h"
 #include "parser/scansup.h"
 #include "utils/builtins.h"
@@ -332,6 +333,8 @@ is_foreign_qual(PlannerInfo *root, RelOptInfo *baserel, Expr *expr)
 static char *
 deparseSql(Oid foreigntableid, PlannerInfo *root, RelOptInfo *baserel)
 {
+	AttrNumber		attr;
+	List		   *attr_used = NIL;
 	List		   *context;
 	StringInfoData	sql;
 	ForeignTable   *table = GetForeignTable(foreigntableid);
@@ -347,24 +350,52 @@ deparseSql(Oid foreigntableid, PlannerInfo *root, RelOptInfo *baserel)
 
 	context = deparse_context_for("foreigntable", foreigntableid);
 
+	/* Collect used columns from restrict information and target list */
+	foreach (lc, baserel->baserestrictinfo)
+	{
+		List		   *l;
+		RestrictInfo   *ri = lfirst(lc);
+
+		l = pull_var_clause((Node *) ri->clause, PVC_RECURSE_PLACEHOLDERS);
+		attr_used = list_union(attr_used, l);
+	}
+	attr_used = list_union(attr_used, baserel->reltargetlist);
+
 	/* deparse SELECT target list */
 	appendStringInfoString(&sql, "SELECT ");
 	first = true;
-	foreach (lc, baserel->reltargetlist)
+	for (attr = baserel->min_attr; attr < baserel->max_attr; attr++)
 	{
-		Var *var = lfirst(lc);
+		Var *var;
 
-		/* system columns cannot be retrieved from remote */
-		if (var->varattno < 0)
+		/* System columns cannot be retrieved from remote. */
+		if (attr < 0)
 			continue;
 
+		/* Separete columns with comma. */
 		if (!first)
 			appendStringInfoString(&sql, ", ");
 		first = false;
-		deparse_var(root, &sql, var);
+
+		/* Use "NULL" for column which isn't in reltargetlist. */
+		foreach (lc, attr_used)
+		{
+			var = lfirst(lc);
+			if (var->varattno == attr)
+				break;
+			var = NULL;
+		}
+
+		if (var != NULL)
+			deparse_var(root, &sql, var);
+		else
+			appendStringInfo(&sql, "NULL");
 	}
 	if (strcmp(sql.data, "SELECT ") == 0)
+	{
+		ereport(DEBUG1, (errmsg("targetlist is empty, retrieve all columns")));
 		appendStringInfo(&sql, "*");
+	}
 
 	/*
 	 * Deparse FROM
-- 
2.39.5