Is it mandatory for a foreign key to be a primary key in another table?

Is it mandatory for a foreign key to be a primary key in another table?

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. So in your case if you make AnotherID unique, it will be allowed.

Can a foreign key be a foreign key in another table?

A foreign key constraint doesn’t have to be linked only to a primary key constraint in another table. Foreign keys can also be defined to reference the columns of a UNIQUE constraint in another table.

Can a primary key be a foreign key in two tables?

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 foreign key not be 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.

Can a table have no primary key?

Every table can have (but does not have to have) a primary key. The column or columns defined as the primary key ensure uniqueness in the table; no two rows can have the same key. The primary key of one table may also help to identify records in other tables, and be part of the second table’s primary key.

Can two relations have same primary key?

Yes. You can have same column name as primary key in multiple tables. Column names should be unique within a table. A table can have only one primary key, as it defines the Entity integrity.

Can foreign key be not unique?

No, Foreign Key in a table doesn’t have to be unique in said table. BUT, as it is the Primary Key of another table, it must be unique in this table. No. No, foreign keys do not have to be unique.

Is primary key always needed?

Every table can have (but does not have to have) a primary key. (The data foreign key column need not exist in the primary key column in the first table.) Non-Identifying Mandatory — means that the column dragged to a second table will not be added to its primary key, and that the relationship is mandatory.

What is relationship between a primary and a foreign key?

A primary key uniquely identifies a record in the relational database table, whereas a foreign key refers to the field in a table which is the primary key of another table. A primary key must be unique and only one primary key is allowed in a table which must be defined, whereas more than one foreign key are allowed in a table.

What is difference between primary key and foreign key?

What is the Difference Between Primary Key and Foreign Key. The main difference between primary key and foreign key is that the primary key is used to identify the records in the table uniquely while the foreign key is used to connect two table together. Most business organizations use databases to store data.

What is difference between “primary key” and “unique key”?

Primary key can be considered as a special case of the unique key. Another difference is that primary keys have an implicit NOT NULL constraint while the unique key does not have that constraint. Therefore, unique key columns may or may not contain NULL values but primary key columns cannot contain NULL values.

What is the difference between primary key and candidate key?

The main difference between primary key and candidate key is that primary key is the minimal set of attributes of the table that helps to identify each row uniquely, while candidate key is a super key with no redundant attributes. Generally, a database of an RDBMS consists of multiple tables.