Can two foreign keys refer to the same primary key?
It is perfectly acceptable for two foreign key columns to reference the same primary key column in another table, since each foreign key value references a different entry in the related table.
Can 2 foreign keys refer to the same primary key?
A foreign key is a database key used to link two tables. … A FOREIGN KEY constraint differs from a PRIMARY KEY constraint in that you can only create one PRIMARY KEY constraint per table, with the option to create multiple FOREIGN KEY constraints per table by clicking multiple primary reference tables.
Can a primary key refer to a foreign key?
A foreign key reference joins two tables when one or more columns containing the primary key value of one table are referenced by one or more columns of another table. This column becomes a foreign key in the second table.
Is it possible to have two foreign keys in a table?
A table can have multiple foreign keys, and each foreign key can have its own parent table. Each foreign key is applied independently of the database system. Therefore, it is possible to establish cascading relationships between tables using foreign keys.
How many foreign keys can a table have?
It is recommended that a table contain no more than 253 FOREIGN KEY constraints and have no more than 253 FOREIGN KEY constraints for reference. Consider the cost of applying FOREIGN KEY constraints when designing your database and applications. Tintu, you have to look at the maximum.
Is it possible to have duplicate foreign keys?
By default, there are no restrictions on the foreign key, the foreign key can be null and double. If you add a single or non-null constraint when creating/editing a table, null/double values are not allowed.
How to add multiple foreign keys?
3 answers. The second block of code in your question: ALTER TABLE ORDERS ADD FOREIGN KEY (customer_sid) REFERENCES CUSTOMER (SID), ADD FOREIGN KEY (customer_sid2) REFERENCES CUSTOMER (SID2) takes care of what you’re trying to do.