Can a foreign key have multiple columns?

MySQL allows us to add a FOREIGN KEY constraint on multiple columns in a table. The condition is that each Foreign Key in the child table must refer to the different parent table.

Can a foreign key have multiple attributes?

A table may have multiple foreign keys, and each foreign key can have a different parent table. Therefore, cascading relationships between tables can be established using foreign keys. A foreign key is defined as an attribute or set of attributes in a relation whose values match a primary key in another relation.

Can a foreign key point to multiple tables?

7 Answers

You could simply create two columns in Ticket, OwnedByUserId and OwnedByGroupId, and have nullable Foreign Keys to each table.
You could create M:M reference tables enabling both ticket:user and ticket:group relationships.

Can any column be a foreign key?

Yes , There can be a foreign key which is unique key in other table as Unique key is subset of primary key but not the exact primary key.

Can a column be a primary and foreign key?

You ‘ll find the answer into this link: Can a database attribute be primary and foreign key? You can create a column having both keys (primary and foreign) but then it will be one to one mapping and add uniqueness to this column.

Can foreign key have NULL values?

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). That is all an FK is by definition.

Can an attribute be both primary and foreign key?

In your case, if there is a one-to-one or a one-to-zero-or-one relationship between User and Employee , then yes, the User_ID in the Employee table can be Foreign Key (FK) and Primary Key (PK) at the same time.

Can a primary key have multiple foreign keys?

Can one primary key have two foreign keys? – Quora. A primary key can be used as a foreign key, it doesn’t possess them. There’s no limit to how many times they can be used.

Can you have a foreign key that isn’t a primary key?

A foreign key can refer to either a unique or a primary key of the parent table. If the foreign key refers to a non-primary unique key, you must specify the column names of the key explicitly.

Does a foreign key have to match a primary key?

The data type of the foreign key does not match that of the primary key. But it also prevents a database from declaring referential integrity to keep a foreign key consistent with its referent.