CREATE TABLE [dbo].[myTable](
	[ColumnA] [uniqueidentifier] NOT NULL,
	[Columnb] [varchar](255) NULL,
 CONSTRAINT [PK_myTable] PRIMARY KEY CLUSTERED 
(
	[ColumnA] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO

ALTER TABLE [dbo].[myTable] ADD  CONSTRAINT [DF__myTable__ColumnA__24485945]  DEFAULT (newsequentialid()) FOR [ColumnA]
GO