Add IF NOT EXISTS for CREATE SERVER and CREATE USER MAPPING

There is still some inconsistency with the error messages surrounding
foreign servers. Some use the word "foreign" and some don't. My
inclination is to remove all such uses of "foreign" on the basis that
the  CREATE/ALTER/DROP SERVER commands don't use the word. However, that
is left for another day. In this patch I have kept to the existing usage
in the affected commands, which omits "foreign".

Anastasia Lubennikova, reviewed by Arthur Zakirov and Ashtosh Bapat.

Discussion: http://postgr.es/m/7c2ab9b8-388a-1ce0-23a3-7acf2a0ed3c6@postgrespro.ru

1 files changed, 33 insertions, 5 deletions

diff --git a/src/backend/commands/foreigncmds.c b/src/backend/commands/foreigncmds.c
index 7f551149d2d..68100df0830 100644
--- a/src/backend/commands/foreigncmds.c
+++ b/src/backend/commands/foreigncmds.c
@@ -879,12 +879,25 @@ CreateForeignServer(CreateForeignServerStmt *stmt)
 
 	/*
 	 * Check that there is no other foreign server by this name.
+	 * Do nothing if IF NOT EXISTS was enforced.
 	 */
 	if (GetForeignServerByName(stmt->servername, true) != NULL)
-		ereport(ERROR,
-				(errcode(ERRCODE_DUPLICATE_OBJECT),
-				 errmsg("server \"%s\" already exists",
-						stmt->servername)));
+	{
+		if (stmt->if_not_exists)
+		{
+			ereport(NOTICE,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("server \"%s\" already exists, skipping",
+							stmt->servername)));
+			heap_close(rel, RowExclusiveLock);
+			return InvalidObjectAddress;
+		}
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("server \"%s\" already exists",
+							stmt->servername)));
+	}
 
 	/*
 	 * Check that the FDW exists and that we have USAGE on it. Also get the
@@ -1152,12 +1165,27 @@ CreateUserMapping(CreateUserMappingStmt *stmt)
 	umId = GetSysCacheOid2(USERMAPPINGUSERSERVER,
 						   ObjectIdGetDatum(useId),
 						   ObjectIdGetDatum(srv->serverid));
+
 	if (OidIsValid(umId))
-		ereport(ERROR,
+	{
+		if (stmt->if_not_exists)
+		{
+			ereport(NOTICE,
+				(errcode(ERRCODE_DUPLICATE_OBJECT),
+				 errmsg("user mapping for \"%s\" already exists for server %s, skipping",
+						MappingUserName(useId),
+						stmt->servername)));
+
+			heap_close(rel, RowExclusiveLock);
+			return InvalidObjectAddress;
+		}
+		else
+			ereport(ERROR,
 				(errcode(ERRCODE_DUPLICATE_OBJECT),
 				 errmsg("user mapping for \"%s\" already exists for server %s",
 						MappingUserName(useId),
 						stmt->servername)));
+	}
 
 	fdw = GetForeignDataWrapper(srv->fdwid);