Can foreign keys hurt query performance

Question

As I understood from this post, there are some scenarios where foreign keys can improve query performance.

I\'ve heard the opposite claim though, that because of refere

Answer 1

I believe the noted post pointed out that putting an index on FK fields improved performance, not simply that a FK relationship improved performance. The existence of a FK on a table should not have any effect on a SELECT query, unless JOIN operations are being done, at which point, the FK relationship AND index on FK fields would improve performance.