2 files changed, 54 insertions, 15 deletions

diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index 6bf6c5a3106..009896bcee7 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -239,21 +239,9 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 	PlannedStmt *plan;
 	QueryDesc  *queryDesc;
 
-	if (stmt->if_not_exists)
-	{
-		Oid			nspid;
-
-		nspid = RangeVarGetCreationNamespace(stmt->into->rel);
-
-		if (get_relname_relid(stmt->into->rel->relname, nspid))
-		{
-			ereport(NOTICE,
-					(errcode(ERRCODE_DUPLICATE_TABLE),
-					 errmsg("relation \"%s\" already exists, skipping",
-							stmt->into->rel->relname)));
-			return InvalidObjectAddress;
-		}
-	}
+	/* Check if the relation exists or not */
+	if (CreateTableAsRelExists(stmt))
+		return InvalidObjectAddress;
 
 	/*
 	 * Create the tuple receiver object and insert info it will need
@@ -401,6 +389,41 @@ GetIntoRelEFlags(IntoClause *intoClause)
 }
 
 /*
+ * CreateTableAsRelExists --- check existence of relation for CreateTableAsStmt
+ *
+ * Utility wrapper checking if the relation pending for creation in this
+ * CreateTableAsStmt query already exists or not.  Returns true if the
+ * relation exists, otherwise false.
+ */
+bool
+CreateTableAsRelExists(CreateTableAsStmt *ctas)
+{
+	Oid			nspid;
+	IntoClause *into = ctas->into;
+
+	nspid = RangeVarGetCreationNamespace(into->rel);
+
+	if (get_relname_relid(into->rel->relname, nspid))
+	{
+		if (!ctas->if_not_exists)
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_TABLE),
+					 errmsg("relation \"%s\" already exists",
+							into->rel->relname)));
+
+		/* The relation exists and IF NOT EXISTS has been specified */
+		ereport(NOTICE,
+				(errcode(ERRCODE_DUPLICATE_TABLE),
+				 errmsg("relation \"%s\" already exists, skipping",
+						into->rel->relname)));
+		return true;
+	}
+
+	/* Relation does not exist, it can be created */
+	return false;
+}
+
+/*
  * CreateIntoRelDestReceiver -- create a suitable DestReceiver object
  *
  * intoClause will be NULL if called from CreateDestReceiver(), in which
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 43f9b01e833..d797b5f53e0 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -435,6 +435,22 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
 		CreateTableAsStmt *ctas = (CreateTableAsStmt *) utilityStmt;
 		List	   *rewritten;
 
+		/*
+		 * Check if the relation exists or not.  This is done at this stage to
+		 * avoid query planning or execution.
+		 */
+		if (CreateTableAsRelExists(ctas))
+		{
+			if (ctas->objtype == OBJECT_TABLE)
+				ExplainDummyGroup("CREATE TABLE AS", NULL, es);
+			else if (ctas->objtype == OBJECT_MATVIEW)
+				ExplainDummyGroup("CREATE MATERIALIZED VIEW", NULL, es);
+			else
+				elog(ERROR,	"unexpected object type: %d",
+					 (int) ctas->objtype);
+			return;
+		}
+
 		rewritten = QueryRewrite(castNode(Query, copyObject(ctas->query)));
 		Assert(list_length(rewritten) == 1);
 		ExplainOneQuery(linitial_node(Query, rewritten),