Question Archive

Which SQL statement is used to retrieve data from a table?

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What does a LEFT JOIN return that an INNER JOIN does not?

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Which operator checks if a value falls within a range inclusively?

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What is the purpose of GROUP BY in SQL?

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What does LIMIT 10 do in a query?

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Which wildcard matches any sequence of characters in a LIKE pattern?

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What does AVG(salary) return?

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Which clause filters groups after aggregation?

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What does the IS NULL condition check?

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Which JOIN type returns only rows with matching values in both tables?

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What does ORDER BY salary DESC do?

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Which aggregate function returns the number of non-NULL values in a column?

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What does SELECT DISTINCT do?

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Which SQL clause filters rows before grouping occurs?

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What is the purpose of `RETURNING` clause in PostgreSQL DML statements?

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What does `WITHIN GROUP (ORDER BY col)` do with ordered-set aggregate functions like `PERCENTILE_CONT()`?

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What is the difference between `UNION` and `UNION ALL` in terms of performance?

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What does `SELECT FOR UPDATE` do in SQL and when would you use it?

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