Where is foreign key in SQL Workbench?

Where is foreign key in SQL?

A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table. The table with the foreign key is called the child table, and the table with the primary key is called the referenced or parent table.

Where are foreign keys stored?

The table that contains the foreign key is considered the child table, and the table that the foreign key references is the parent table.

Is foreign key can be null?

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).

Can a primary key be a foreign key?

Yes, it is legal to have a primary key being a foreign key. This is a rare construct, but it applies for: a 1:1 relation. The two tables cannot be merged in one because of different permissions and privileges only apply at table level (as of 2017, such a database would be odd).

What is a foreign key example?

A foreign key is a set of attributes in a table that refers to the primary key of another table. The foreign key links these two tables. … For example, a table called TEAM may have an attribute, MEMBER_NAME, which is a foreign key referencing a candidate key, PERSON_NAME, in the PERSON table.

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Does foreign key have to be 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.

Why foreign keys are not redundant?

Essentially, primary and foreign keys are used as a way to constrain or link related data in a database. This ensures that data remains consistent and that the database contains no redundant data. For example, if you delete a table (or even a row in a table) that other tables rely on, the redundant data is removed.

What is foreign key in a database?

Foreign keys. A foreign key is a column or a set of columns in a table whose values correspond to the values of the primary key in another table. In order to add a row with a given foreign key value, there must exist a row in the related table with the same primary key value.