There is a restriction that we must have only one primary key per table. We can have composite primary key by defining primary key over 2 or more columns. Actually,, a primary key uniquely defines the table and if we have two or more columns which follow unique and not null features why can't we have two primary keys?? I want to know what is the main reason behind having only one primary key in a table??
SQL Server only allows one primary key. It's like having two children and saying they are both first born; It doesn't make sense. In reality a PK is only a unique constraint on a non-nullable column, but it has the special distinction on being "primary." Additionally, people tend to associate the clustering of a table on the primary key, although that is not a requirement for a PK.