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Thomas Joseph Meneses
9,838 PointsDo foreign keys affect SQL JOIN operations?
Learning about normalization and joining tables, as well as about foreign keys, really piqued my programmer's curiosity. Both concepts seem to go hand-in-hand, particularly that both mean to define and then use table relationships. And yet wherever I looked, no one seemed to be asking this question (not even in the almighty Stack Overflow).
Can the constraint of having foreign keys allow in some way the SQL engine to JOIN the respective parent and child tables in a way that's somehow better than not having foreign keys defined at all? Although the constraints are defined, it seems as though a JOIN still requires the coder to set the related columns through ON [table1].[col1] = [table2].[col2].
If there is now way to depend on the previously defined foreign key when doing a JOIN, then it is in my opinion a violation of DRY since you already defined the relationship, and yet need to define it again when JOINing the related tables.