Pattern for creating tables that can only ever have one row.

SingleRowTable.sql

CREATE TABLE ConfigTable(
	[ConstrainToSingleRow] [BIT] NOT NULL DEFAULT ((1)),
	SomeValue [INT] NULL,
	A_String [VARCHAR](10) NULL,
	Flag1 [BIT] NULL DEFAULT ((0)),
	Flag2 [BIT] NULL DEFAULT ((0)),
	A_decimal [DECIMAL](9, 2) NULL,
PRIMARY KEY CLUSTERED 
(
	[ConstrainToSingleRow] ASC
)

) ON [PRIMARY]

ALTER TABLE ConfigTable  WITH CHECK ADD CHECK  (([ConstrainToSingleRow]=(1)))
GO