Unione colonne verticalmente in SQL

SELECT 
    [PR].[Id],
    [PR].[Name],
    [PR].[GroupId],
    [GR].[Title] AS [Group],
    [PR].[CategoryId],
    [CA].[Title] AS [Category],
    ISNULL([PD].[Id],
    CAST(-1 AS BIGINT)) AS [ProductDealerId],
    ISNULL([D].Id,
    CAST(-1 AS BIGINT)) as DealerId,
    ISNULL([D].Name,
    CAST('HaveNotDealer' AS NVARCHAR)) as DealerName,
    ISNULL(PD.LastSale,
    CAST('0001-01-01 00:00:01' AS DATETIME2)) as LastSale,
    ISNULL([PD].Number,
    CAST(0 AS BIGINT)) as SaleNumber

FROM [dbo].[Product] AS [PR]
INNER JOIN [dbo].[Group] AS [GR] ON [PR].[GroupId] = [GR].[Id]
INNER JOIN [dbo].[Category] AS [CA] ON [PR].[CategoryId] = [CA].[Id]
LEFT OUTER JOIN [dbo].[ProductDealer] AS [PD] ON [PR].[Id] = [PD].[ProductId]
LEFT OUTER JOIN [dbo].[Dealer] AS [D] ON [PD].DealerId = [D].Id