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Are foreign keys required fields?
They are not required, strictly speaking, but the benefits are huge. I’m fairly certain that FogBugz does not have foreign key constraints in the database.
Can a table exist without foreign key?
You don’t have to configure a foreign key constraint on a column just because it refers to another column. You could instead configure two tables such that one refers to the other, but without any defined foreign key. You could add a UserId column to Customer and still use it for querying purposes.
What are the requirements for a foreign key field?
The foreign key must be a primary key on at least one of the tables.
Should I use a foreign key in MySQL?
Foreign keys aren’t required to have a working relational database (in fact MySQL’s default storage engine doesn’t support FKs), but they are definitely essential to avoid broken relationships and orphan rows (ie. referential integrity).
Why are there no foreign keys in databases?
Tables relations are not clear Another, less visible, negative effect of lack of foreign keys in a database is that people who don’t know the schema have a hard time finding the right tables and figuring out table relations. This may lead to serious problems with querying and reporting from the database.
How does the FOREIGN KEY constraint work in SQL?
To understand the concept of the FOREIGN KEY constraint in SQL, you can think of it as a reference link between tables that are known as the primary (or parent) and foreign (or child) tables. The foreign table references one or more columns (the primary key, which can be one or more columns) in the primary table; that is how the link is created.
What are the negative effects of lack of foreign keys?
Another, less visible, negative effect of lack of foreign keys in a database is that people who don’t know the schema have a hard time finding the right tables and figuring out table relations. This may lead to serious problems with querying and reporting from the database. Why databases don’t have foreign keys?
Are there indexes for foreign keys in SQL Server?
@John – Other databases may automatically create indexes for foreign keys, but SQL Server does not. In SQL Server, foreign key relationships are only constraints. You must defined your index on foreign keys separately (which can be of benefit.)