Question
Why are OLTP systems usually normalized?
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Answer
To reduce redundancy and support efficient transactions.
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Question
Why would you use ETL when combining data from multiple sources?
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Answer
To clean, standardize, deduplicate, and load data into a target.
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Question
How does HAVING differ from WHERE in SQL?
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Answer
WHERE filters rows; HAVING filters grouped results.
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Question
How does a LEFT JOIN differ from an INNER JOIN?
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Answer
LEFT JOIN keeps all left-table rows; INNER JOIN keeps only matches.
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