______ is NOT a type of constraint in SQL language?
- FOREIGN KEY
- PRIMARY KEY
- ALTERNATE KEY
Explanation: ALTERNATE KEY is a key associated with one or more columns to identify each row in a table uniquely. If a table with one or more candidate keys, then the keys other than the primary key is an alternate key. Since the alternate key is a part of the candidate key, it is not a constraint in SQL. Hence, option D is the correct choice.