To delete Foreign Key Constraint from existing column, apply this sql Transact-SQL Query:
use myDB_name
alter table Countries
drop constraint FK_ContinentID
To Add a new Foreign Key Constraint to existing column, apply this Transact-SQL Query:
use myDB_name
alter table Countries add constraint FK_RegionID foreign key (RegionID) references Regions(RegionID) on update cascade on delete no action
(on update) and (on delete) are the action taken in the referre table when data changes in the referenced tabe.
Environment:
You can apply such Foreign Key changes (or other Transact-SQL) either directly via your Visual Studio or via Microsoft SQL Server Management Studio.