When designing a database table what is the foreign key?
The foreign key is the anchor on the many side of a one-to-many (1:M) relationship, much as the primary or candidate key is the anchor on the one side of this relationship. A foreign key is the linchpin that makes sure you don’t enter invalid data into a table.
What is a foreign key database design?
A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It acts as a cross-reference between tables because it references the primary key of another table, thereby establishing a link between them.
Can a database have a foreign key reference?
Cross-database foreign key references are not supported. Foreign key Database2.table2. Could not create constraint. See previous errors. How do I do that since the tables are in different databases. You would need to manage the referential constraint across databases using a Trigger.
Can a foreign key be used on a parent table?
Although you cannot use a foreign key in this situation, there are workarounds – you can use either triggers or UDFs wrapped in check constraints. Either way, your data integrity is not completely watertight: if the database with your parent table crashes and you restore it from a backup, you may easily end up with orphans.
Can a cross database foreign key be used in SQL Server?
It can be disabled and reenabled when necessary same as foreign keys and rechecked after a database2 restore. The short answer is that SQL Server (as of SQL 2008) does not support cross database foreign keys–as the error message states. While you cannot have declarative referential integrity (the FK), you can reach the same goal using triggers.
What are the rules for referential integrity in SQL?
To enforce referential integrity (rules about the relationships between the primary and foreign keys of tables), use primary and foreign key constraints (the PRIMARY KEY and FOREIGN KEY keywords of ALTER TABLE and CREATE TABLE).