Can you use a non-primary key as a foreign key?
Yes, a foreign key can reference a non-primary key which is unique. A FOREIGN KEY constraint does not have to be linked only to a PRIMARY KEY constraint in another table; it can also be defined to reference the columns of a UNIQUE constraint in another table.
Can a primary key also be a foreign key?
Foreign keys are almost always “Allow Duplicates,” which would make them unsuitable as Primary Keys. It is perfectly fine to use a foreign key as the primary key if the table is connected by a one-to-one relationship, not a one-to-many relationship.
Can we create foreign key on composite primary key?
Is it possible to use one of the attributes of a composite primary key as a foreign key? Yes, this is quite common and perfectly valid.
Can other than primary key values be used as foreign key in another table?
Primary keys always need to be unique, foreign keys need to allow non-unique values if the table is a one-to-many relationship. It is perfectly fine to use a foreign key as the primary key if the table is connected by a one-to-one relationship, not a one-to-many relationship.
Can a composite primary key be a foreign key?
Is it OK for a table to only have a foreign key?
Can we have composite foreign key in Oracle?
To apply composite foreign key you need to have composite primary key……means in one table. What you are doing is creating a composite foreign key with two different primary keys. You are probably making two columns foreign key which refer two different primary keys.
Can a table have both primary key and composite key?
A Table can have a Composite Primary Key which is a primary key made from two or more columns. For example: CREATE TABLE userdata ( userid INT, userdataid INT, info char(200), primary key (userid, userdataid) ); Update: Here is a link with a more detailed description of composite primary keys.
Can a table have 3 primary keys?
A table can only ever have a one primary key. It is not possible to create a table with two different primary keys. You can create a table with two different unique indexes (which are much like a primary key) but only one primary key can exist.
What is a foreign key in Oracle?
Summary: in this tutorial, you will learn how to use the Oracle foreign key to establish the relationship between tables. A foreign key is all about the relationship. Let’s start with an example to clearly understand its concept.
How to create a foreign key to a non-primary key?
Show activity on this post. If you really want to create a foreign key to a non-primary key, it MUST be a column that has a unique constraint on it. A FOREIGN KEY constraint does not have to be linked only to a PRIMARY KEY constraint in another table; it can also be defined to reference the columns of a UNIQUE constraint in another table.
How to create a foreign key with more than one field?
We could also create a foreign key with more than one field as in the example below: In this example, our foreign key called fk_foreign_comp references the supplier table based on two fields – the supplier_id and supplier_name fields. The syntax for creating a foreign key in an ALTER TABLE statement is:
Can a FOREIGN KEY constraint be linked to a prime key?
A FOREIGN KEY constraint does not have to be linked only to a PRIMARY KEY constraint in another table; it can also be defined to reference the columns of a UNIQUE constraint in another table. Show activity on this post. Yes, You would typically at least index it.