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Are foreign keys allowed in 3NF?
3NF requires that every non-key attribute of a relation is non-transitively dependent on every candidate key. So if the foreign key you are referring to consists of a non-key attribute or attributes then the answer to your first question is yes.
Can a database have two foreign keys?
A table may have multiple foreign keys, and each foreign key can have a different parent table. Each foreign key is enforced independently by the database system. Therefore, cascading relationships between tables can be established using foreign keys.
What is foreign key in 3NF?
Foreign Key references the primary key of another Table! It helps connect your Tables. A foreign key can have a different name from its primary key. It ensures rows in one table have corresponding rows in another. Unlike the Primary key, they do not have to be unique.
Can a table have two foreign keys in mysql?
A table can have multiple foreign keys and no composite keys. A composite key simply means that there are two or more columns making up the key value.
How do I convert 2NF to 3NF?
The normalization of 2NF relations to 3NF involves the removal of transitive dependencies. If a transitive dependency exists, we remove the transitively dependent attribute(s) from the relation by placing the attribute(s) in a new relation along with a copy of the determinant. Consider the examples given below.
Can we add two foreign keys in table?
A Foreign Key is a database key that is used to link two tables together. The FOREIGN KEY constraint differs from the PRIMARY KEY constraint in that, you can create only one PRIMARY KEY per each table, with the ability to create multiple FOREIGN KEY constraints in each table by referencing multiple parent table.
Can a single field be a foreign key to two different tables?
No, you can’t have a single field as a foreign key to two different tables. How would you tell where to look for the key? You would at least need a field that tells what kind of user it is, or two separate foreign keys.
Can a relation be in 3NF with multiple foreign keys?
To speak directly to the question, yes, a relation can be in 3NF even if it has multiple foreign keys. The key (cough) point of 3NF is to remove transitive dependencies, not to reduce the number of foreign keys. To put it another way, there’s no such thing as “I have too many foreign keys” normal form.
Can a foreign key be used as a primary key?
You could also put the information that is common for all users in one table and have separate tables for the information that is specific for the user types, so that you have a single table with user id as primary key. A foreign key can only reference a single primary key, so no. However, you could use a bridge table:
How are foreign keys used in association tables?
But FKs (foreign keys) are between tables, so they do not affect what normal forms a table is in. (Some diagramming styles have lines that are FKs. Others have lines that are relationships represented by “association” tables. Some have both kinds of lines.