I'm adding a table and subclass table to my DB. (Subclass table = table where the primary key joins to the primary key of another table, to give extra row information to some subset of the rows ...

Foreign keys enforce table relationships, for example (in the case of school enrollments) forbidding you from adding a non-existent student to a class roster, or from deleting a class roster that ...

The ease and ubiquity of SQL have even led the creators of many “ NoSQL ” or non-relational data stores, such as Hadoop, to adopt subsets of SQL or come up with their own SQL-like query languages.