SQL Quiz
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DATA QUALITY AND DEBUGGING
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A child table has a composite foreign key (region_id, account_id). Five rows contain these pairs: (1, 2), (1, NULL), (NULL, 2), (3, 4), and (NULL, NULL). The parent contains (1, 2) but not (3, 4). A key is incomplete if either component is NULL. An orphan must have both components present but no matching parent pair.
Which classification logic produces 33 incomplete keys and 11 orphan?
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