Can you reference a foreign key?

Can you reference a foreign key?

A foreign key can reference any field defined as unique. If that unique field is itself defined as a foreign key, it makes no difference. If it is a unique field, it can also be the target of another FK.

What must a foreign key reference?

5 Answers. In the relational model of data, a foreign key must reference a candidate key. In almost all SQL dbms, a foreign key must reference a candidate key.

Is references the same as foreign key?

The only and most important difference between the two keywords ‘FOREIGN KEY” and “REFERENCES” keywords is though both of them make the data to be child data of the parent table, the “FOREIGN KEY” is used to create a table level constraint whereas REFERENCES keyword can be used to create column level constraint only.

Can foreign key have multiple references?

A: No, it can’t. That is, not technically. Technically, a foreign key is a constraint on a (set of) column(s): the values in that (set of) column(s) are not allowed to be anything else than what is listed in some (other) table: actually, the primary key (or an alternate key) of that table.

Does a foreign key need to reference a primary key?

A foreign key must refer to an entire primary key, and not just part of it. Consider a Department table with a primary key of company_name + department_name. An Employee table should only refer to both attributes and not to department_name alone.

Can we add foreign key without primary key?

Yes. You can FK reference any UNIQUE KEY constraint (one or more columns).

Can foreign key be null SQL?

Short answer: Yes, it can be NULL or duplicate. I want to explain why a foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table).

Is foreign key must be primary key?

Does every table need a foreign key?

Note that foreign keys are not mandatory, and a table may have no foreign keys. Conversely, every column in a table may have a foreign key constraint.

What is the advantage of foreign key?

The FOREIGN KEY constraint is crucial to relational database design. It lets us link the data according to our needs. As it creates some dependencies between the columns of primary and foreign tables, it also lets us decide what to do ON UPDATE and ON DELETE actions performed on the rows of the primary table.