DECLARE @LoginPlatforms TABLE (
	[Platform] NVARCHAR(20)
)

INSERT INTO @LoginPlatforms ([Platform])
VALUES
	('Guest'),
	('Microsoft');

MERGE [user].[LoginPlatform] as t
USING @LoginPlatforms as s
ON t.[Platform] = s.[Platform]
WHEN NOT MATCHED THEN
	INSERT ([Platform])
	VALUES (s.[Platform]);