Databases quiz
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Which key points to a row in another table?
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More questions about Databases
These visible examples show the question style. LearnClash turns the full topic into ranked duels and spaced repetition.
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Which database engine is in every iPhone and Android phone?
Answer: SQLite
Why: By its makers' estimate, more than one trillion SQLite databases are in active use around the world.
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How do you undo an unfinished SQL transaction?
Answer: ROLLBACK
Why: COMMIT is the opposite move: it ends the transaction by making its changes permanent instead of discarding them.
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What is reading another transaction's unsaved changes called?
Answer: Dirty read
Why: Read Uncommitted is the isolation level that permits dirty reads, while Read Committed and stricter levels prevent them.
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Which language says what data you want, not how to get it?
Answer: SQL
Why: The database's query optimizer weighs the possible plans for each SQL query and picks the one it judges most efficient.
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When do extra indexes slow a database down?
Answer: On writes
Why: Each index has to be updated whenever the table changes, so a table with more indexes takes longer to change.
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What does 'relation' mean in a relational database?
Answer: A table
Why: Codd borrowed 'relation' from mathematics, where it means a set of tuples, and SQL shows one as a table with a row per tuple.
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