v1-0001-COPY-materialized_view-TO.patch

From a618e72ae33b6688e75dbcfd5674b558e17ee269 Mon Sep 17 00:00:00 2001
From: jian he <jian.universality@gmail.com>
Date: Tue, 28 Jan 2025 10:46:03 +0800
Subject: [PATCH v1 1/1] COPY materialized_view TO

context: https://postgr.es/m/8967.1353167301@sss.pgh.pa.us
context: https://www.postgresql.org/message-id/flat/20121116162558.90150%40gmx.com
discussion: https://postgr.es/m/CACJufxHVxnyRYy67hiPePNCPwVBMzhTQ6FaL9_Te5On9udG=yg@mail.gmail.com
---
 src/backend/commands/copyto.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 99cb23cb34..13506023f8 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -380,11 +380,13 @@ BeginCopyTo(ParseState *pstate,
 							RelationGetRelationName(rel)),
 					 errhint("Try the COPY (SELECT ...) TO variant.")));
 		else if (rel->rd_rel->relkind == RELKIND_MATVIEW)
-			ereport(ERROR,
-					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("cannot copy from materialized view \"%s\"",
-							RelationGetRelationName(rel)),
-					 errhint("Try the COPY (SELECT ...) TO variant.")));
+		{
+			if (!RelationIsPopulated(rel))
+				ereport(ERROR,
+						errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						errmsg("cannot copy from materialized view when the materialized view is not populated"),
+						errhint("Use the REFRESH MATERIALIZED VIEW command populate the materialized view first."));
+		}
 		else if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-- 
2.34.1