1. What is GROUP BY ? Junior A. COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column B. groups rows sharing a value so aggregates are computed per group C. every selected non-aggregated column must also appear in the GROUP BY clause D. filters groups after aggregation, whereas WHERE filters rows before it
2. Which term means: "groups rows sharing a value so aggregates are computed per group"? Junior A. COUNT / SUM / AVG B. GROUP BY column rule C. GROUP BY D. COUNT(*) vs COUNT(col)
3. Which statement is correct? Junior A. GROUP BY — filters groups after aggregation, whereas WHERE filters rows before it B. GROUP BY — groups rows sharing a value so aggregates are computed per group C. GROUP BY — COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column D. GROUP BY — returns the first non-NULL value from its arguments
4. What is HAVING ? Mid A. groups rows sharing a value so aggregates are computed per group B. filters groups after aggregation, whereas WHERE filters rows before it C. aggregate functions returning row count, total, and mean over a group D. COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column
5. Which term means: "filters groups after aggregation, whereas WHERE filters rows before it"? Mid A. COALESCE B. COUNT(*) vs COUNT(col) C. COUNT / SUM / AVG D. HAVING
6. Which statement is correct? Mid A. HAVING — aggregate functions returning row count, total, and mean over a group B. HAVING — COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column C. HAVING — every selected non-aggregated column must also appear in the GROUP BY clause D. HAVING — filters groups after aggregation, whereas WHERE filters rows before it
7. What is COUNT / SUM / AVG ? Junior A. returns the first non-NULL value from its arguments B. aggregate functions returning row count, total, and mean over a group C. every selected non-aggregated column must also appear in the GROUP BY clause D. groups rows sharing a value so aggregates are computed per group
8. Which term means: "aggregate functions returning row count, total, and mean over a group"? Junior A. GROUP BY column rule B. COUNT(*) vs COUNT(col) C. COUNT / SUM / AVG D. HAVING
9. Which statement is correct? Junior A. COUNT / SUM / AVG — aggregate functions returning row count, total, and mean over a group B. COUNT / SUM / AVG — every selected non-aggregated column must also appear in the GROUP BY clause C. COUNT / SUM / AVG — returns the first non-NULL value from its arguments D. COUNT / SUM / AVG — COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column
10. What is GROUP BY column rule ? Mid A. aggregate functions returning row count, total, and mean over a group B. groups rows sharing a value so aggregates are computed per group C. COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column D. every selected non-aggregated column must also appear in the GROUP BY clause
11. Which term means: "every selected non-aggregated column must also appear in the GROUP BY clause"? Mid A. COALESCE B. GROUP BY C. GROUP BY column rule D. COUNT(*) vs COUNT(col)
12. Which statement is correct? Mid A. GROUP BY column rule — aggregate functions returning row count, total, and mean over a group B. GROUP BY column rule — COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column C. GROUP BY column rule — returns the first non-NULL value from its arguments D. GROUP BY column rule — every selected non-aggregated column must also appear in the GROUP BY clause
13. What is **COUNT(*) vs COUNT(col)**? Mid A. aggregate functions returning row count, total, and mean over a group B. groups rows sharing a value so aggregates are computed per group C. COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column D. returns the first non-NULL value from its arguments
14. Which term means: "COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column"? Mid A. COALESCE B. GROUP BY column rule C. HAVING D. COUNT(*) vs COUNT(col)
15. Which statement is correct? Mid A. COUNT(*) vs COUNT(col) — returns the first non-NULL value from its arguments B. COUNT(*) vs COUNT(col) — COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column C. COUNT(*) vs COUNT(col) — every selected non-aggregated column must also appear in the GROUP BY clause D. COUNT(*) vs COUNT(col) — groups rows sharing a value so aggregates are computed per group
16. What is COALESCE ? Mid A. every selected non-aggregated column must also appear in the GROUP BY clause B. COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column C. groups rows sharing a value so aggregates are computed per group D. returns the first non-NULL value from its arguments
17. Which term means: "returns the first non-NULL value from its arguments"? Mid A. COUNT / SUM / AVG B. GROUP BY C. GROUP BY column rule D. COALESCE
18. Which statement is correct? Mid A. COALESCE — COUNT(*) counts all rows; COUNT(col) counts only non-NULL values of that column B. COALESCE — returns the first non-NULL value from its arguments C. COALESCE — groups rows sharing a value so aggregates are computed per group D. COALESCE — every selected non-aggregated column must also appear in the GROUP BY clause