Plansplaining, part 13. Foreign keys, part 2
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Welcome to part thirteen of the plansplaining series. In this part I continue the exploration of how execution plans check foreign keys on data modification. In the previous part, we looked at foreign key checking when data is inserted. Inserts in the referencing (child) table can, by definition, not cause foreign key violations, so no checking is done in those cases. But for inserts in the referenced (parent) table, SQL Server needs to check that the inserted value does indeed exist. We saw how both the Nested Loops and the Merge Join operators have some specific optimizations to do that…
