left outer join

SELECT dbo.订单.Id AS 订单ID, ISNULL(dbo.产品.Price, 0) + ISNULL(dbo.服务.Price, 0) AS 价格, ISNULL(dbo.产品.Name, '') + ISNULL(dbo.服务.Name, '') AS 名称 FROM dbo.订单 LEFT OUTER JOIN dbo.服务 ON dbo.订单.ServiceId = dbo.服务.Id LEFT OUTER JOIN dbo.产品 ON dbo.订单.ProductId = dbo.产品.Id