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Senior data roles probe beyond syntax into internals: how indexes work, how transactions isolate, and how you'd diagnose a slow query at 2 AM. These questions separate practitioners from readers.
Key Points
- How does a B-tree index work, and what is the leftmost prefix rule?
- Explain clustered vs secondary indexes in InnoDB
- Isolation levels: what anomalies does each prevent? What's MySQL's default (REPEATABLE READ)?
- RANK vs DENSE_RANK vs ROW_NUMBER — and a top-N-per-group query on the spot
- Walk through diagnosing a slow query with EXPLAIN ANALYZE
- How does replication work, and what is replica lag?