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How does a foreign key improve query performance?
Any performance implications/improvements will be specific to the database technology being used and are secondary to the purpose of a foreign key. It is good practice in SQL Server to ensure that all foreign keys have at least a non clustered index on them. I hope this clears things up for you but please feel free to request more details.
Is it bad to have foreign keys in a database?
After having worked at various employers I’ve noticed a trend of “bad” database design with some of these companies – primarily the exclusion of Foreign Keys Constraints. It has always bugged me that these transactional systems didn’t have FK’s, which would’ve promoted referential integrity.
When to use foreign key constraints in SQL?
Using the “built-in layer” of foreign key constraints seems to make the most sense, but if you have a rock solid service layer responsible for the same thing then it has freedom to break the rules if necessary. Personally I use foreign key constraints and engineer my apps so they don’t have to break the rules.
Can a foreign key be null in SQL?
If you still wanted foreign key constraints, you would have to have two different fields for the same mutally exclusive information and allow them to be null.
When to use FOREIGN KEY constraint in Java?
Foreign key constraint improve performance at the time of reading data but at the same time it slows down the performance at the time of inserting / modifying / deleting data.
Can a foreign key slow down a P.P.S?
P.P.S. However having a foreign key (or other constraints) can slow down INSERT/UPDATE/DELETE s unless you have a non-clustered index on this column Thanks for contributing an answer to Stack Overflow!
What is the purpose of a foreign key?
A foreign key is a DBMS concept for ensuring database integrity. Any performance implications/improvements will be specific to the database technology being used and are secondary to the purpose of a foreign key.