Hi I’ve set up two very basic tables. One table will act as a look up, with an identity field as a primary key. The other table uses the look up ID as a foreign key.
I have created a relationship constraint so now I cannot delete from the look up if the foreign key is used in the “main” table.
However my issue is i can add a record with a foreign key that doesn’t exist.
To my way of thinking this shouldn’t be allowed, can anyone tell me what setting I need to use to enforce this and whether this is typical database design or not?
Thanks Dave
You way of thinking is correct. Good database design provides some way of enforcing what is called “Referential Integrity”. This is simply a buzzword for the concept you have derived on your own. Namely that a foreign key should be rejected if it refers to a non existent row. For a general discussion of referential integrity, see the following Wikipedia article. It’s short.
http://en.wikipedia.org/wiki/Referential_integrity
Some pprogrammers would like to enforce referential integrity inside their programs. In general, it’s a much better plan to define a referential integrity constraint inside the database, and let the DBMS do the enforcement. It’s easier, it’s faster, and it’s more effective.
The SQL Data Definition Language (DDL) provides a way to declare a foreign key constraint when you create a table. The syntax differs a little between different dialects of SQL, but it’s basically the same idea in all of them. Here’s a capsule summary.
http://www.w3schools.com/sql/sql_foreignkey.asp
The documentation for SQL Server should have a description of the referential integrity constraint under the CREATE TABLE command.