Can a foreign key reference 2 tables?
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 one foreign key point to multiple tables?
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.
Can a foreign key be used on two tables?
A foreign key cannot reference two tables. Assuming you don’t want to correct your design by merging members_company1 and members_company2 tables, the best approach would be to: Add two columns called member_company1_id and member_company2_id to your profiles table and create two foreign keys to the two tables and allow nulls.
How to maintain referential integrity of foreign keys?
Solution 2: This solution allows referential integrity to be maintained: 1. Create a second foreign key field in ‘Deductions’ table , allow Null values in both foreign keys, and create normal foreign keys: Integrity is only checked if the column is not null, so you can maintain referential integrity.
How are foreign keys made primary keys in SQL Server?
(The respective columns in the other two tables are made primary keys accordingly.) The CK_Ticket_GroupUser check constraint ensures that only one of the two foreign key columns contains a reference (the other being NULL, that’s why both have to be nullable).
When to use a foreign key to refer to an employee?
To refer to an employee of any kind (ce or sn), refer to the employees table. That is, the foreign key you had trouble with should refer to that table! You can probably add two foreign key constraints (honestly: I’ve never tried it), but it’d then insist the parent row exist in both tables.