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MySQL quiz questions and answers
Review all 5 questions at your own pace. Open each answer to see the correct response and a concise explanation of the concept.
1What does an index usually improve?
Correct answer
Read query lookup speed
Indexes help MySQL find rows faster, though they add write and storage cost.
2Which SQL clause filters grouped results?
Correct answer
HAVING
HAVING filters after GROUP BY aggregation, while WHERE filters rows before grouping.
3What does an INNER JOIN return?
Correct answer
Rows with matching values in both tables
INNER JOIN returns records that satisfy the join condition in both tables.
4What is a transaction useful for?
Correct answer
Keeping multiple database operations atomic
Transactions ensure related changes either all commit or all roll back.
5Which command helps inspect how MySQL will run a query?
Correct answer
EXPLAIN
EXPLAIN shows the query plan, including indexes and join strategy.