Multi-level constraints

I am not able to paste the image. What I can do is share the text of the tables with foreign keys.

CREATE TABLE [dbo].[SkillName](
[SkillName] [varchar](50) NOT NULL,
CONSTRAINT [PK_SkillName] PRIMARY KEY CLUSTERED
(
[SkillName] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Trade](
[TradeName] [varchar](50) NOT NULL,
[SkillName] [varchar](50) NOT NULL,
CONSTRAINT [PK_Trade] PRIMARY KEY CLUSTERED
(
[TradeName] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Worker](
[WorkerName] [varchar](50) NOT NULL,
[TradeName] [varchar](50) NOT NULL,
CONSTRAINT [PK_Worker] PRIMARY KEY CLUSTERED
(
[WorkerName] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[Trade] WITH CHECK ADD CONSTRAINT [FK_Trade_SkillName] FOREIGN KEY([SkillName])
REFERENCES [dbo].[SkillName] ([SkillName])
GO
ALTER TABLE [dbo].[Trade] CHECK CONSTRAINT [FK_Trade_SkillName]
GO
ALTER TABLE [dbo].[Worker] WITH CHECK ADD CONSTRAINT [FK_Worker_Trade] FOREIGN KEY([TradeName])
REFERENCES [dbo].[Trade] ([TradeName])
GO
ALTER TABLE [dbo].[Worker] CHECK CONSTRAINT [FK_Worker_Trade]
GO