IF not EXISTS( SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'ContractHistory' AND  COLUMN_NAME = 'CH_ID')
begin
	alter table ContractHistory add CH_ID	int references ContractHistory(ID) null
end
;
IF not EXISTS( SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'ContractHistory' AND  COLUMN_NAME = 'CH_ID_Parent')
begin
	alter table ContractHistory add CH_ID_Parent	int references ContractHistory(ID) null
end