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
Which aggregate function returns the total number of rows, including those with NULL values in the counted column?
Answer: COUNT(*)
COUNT(*) counts every row regardless of NULLs, while COUNT(column) skips NULLs.
What does AVG(salary) ignore when computing the average?
Answer: NULL values
AVG ignores NULL rows entirely, dividing the sum by the count of non-NULL values.
In a query with GROUP BY department, which column can appear in SELECT without being aggregated?
Answer: department
Only the grouping column(s) may appear ungrouped and unaggregated in the SELECT list.
Which clause filters groups based on an aggregate condition like SUM(amount) > 1000?
Answer: HAVING
HAVING applies conditions to grouped results after aggregation, unlike WHERE.
What is the result of COUNT(DISTINCT city) on a column with values 'NY','NY','LA',NULL?
Answer: 2
DISTINCT counts unique non-NULL values, so 'NY' and 'LA' give 2.
Which function returns the largest value in a numeric column?
Answer: MAX
MAX returns the highest value among the rows in each group or set.
In the logical order of execution, when is GROUP BY processed relative to WHERE?
Answer: After WHERE
WHERE filters rows first, then GROUP BY groups the remaining rows.