Aggregate Functions and Grouping Flashcards
7 cards from real SQL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Aggregate Functions and Grouping flashcards as text
What does GROUP BY GROUPING SETS((a),(b)) produce?
Answer: Separate aggregations grouped by a and by b
GROUPING SETS computes multiple independent groupings in one query.
Which clause can use a column alias defined in SELECT in many databases?
Answer: HAVING
Some databases allow SELECT aliases in HAVING since it runs after SELECT logically in those engines.
What is returned by AVG over the values 2, 4, NULL, 6?
Answer: 4
AVG ignores NULL, so (2+4+6)/3 = 4.
Which is true about ORDER BY in a grouped query?
Answer: It sorts the final grouped result
ORDER BY sorts the output after grouping and aggregation are complete.
What does the MIN function return for a group of dates?
Answer: The earliest date
MIN returns the smallest value, which for dates is the earliest one.
Which query finds departments whose average salary exceeds 50000?
Answer: GROUP BY dept HAVING AVG(salary)>50000
Filtering on an aggregate per group requires HAVING after GROUP BY.
What happens if you use SELECT name, COUNT(*) FROM t without a GROUP BY in strict mode?
Answer: Raises an error or undefined behavior
Mixing a non-aggregated column with an aggregate without GROUP BY is invalid in strict SQL.