Question

What are the principal of foriegn key constraints?

Answer 1

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.

Answer 2

A foreign key (FK) is a column or combination of columns that is used to establish and enforce a link between the data in two tables. You can create a foreign key by defining a FOREIGN KEY constraint when you create or modify a table.

In a foreign key reference, a link is created between two tables when the column or columns that hold the primary key value for one table are referenced by the column or columns in another table. This column becomes a foreign key in the second table.

For example, the Sales.SalesOrderHeader table in the AdventureWorks2008R2 database has a link to the Sales.SalesPerson table because there is a logical relationship between sales orders and salespeople. The SalesPersonID column in the SalesOrderHeadertable matches the primary key column of the SalesPerson table. The SalesPersonID column in the SalesOrderHeader table is the foreign key to the SalesPerson table.

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