A study of 6,008 real database schemas from public repositories found that 45.1% of foreign keys lack covering indexes, with significant variation across tools: Rails creates indexes by default (3.5% unindexed), while design tools like DBML and pgModeler leave ~80% unindexed. Additionally, 24.5% of schemas declare no foreign keys at all, suggesting relationships are often enforced in application code rather than the database.