Table EXAM_RESULTS

STU ID	FNAME	LNAME	EXAM ID	EXAM_SCORE
10	LAURA	LYNCH	1	90
10	LAURA	LYNCH	2	85
11	GRACE	BROWN	1	78
11	GRACE	BROWN	2	72
12	JAY	JACKSON	1	95
12	JAY	JACKSON	2	92
13	WILLIAM	BISHOP	1	70
13	WILLIAM	BISHOP	2	100
14	CHARLES	PRADA	2	85

Which SQL statement do we use to find out how many students took each exam?

1. SELECT COUNT(DISTINCT STU_ID) FROM EXAM_RESULTS GROUP BY EXAM_ID;
2. SELECT EXAM_ID, MAX(STU_ID) FROM EXAM_RESULTS GROUP BY EXAM_ID;
3. SELECT EXAM_ID, COUNT(DISTINCT STU_ID) FROM EXAM_RESULTS GROUP BY EXAM_ID;
4. SELECT EXAM_ID, MIN(STU_ID) FROM EXAM_RESULTS GROUP BY EXAM_ID;

SELECT EXAM_ID, COUNT(DISTINCT STU_ID) FROM EXAM_RESULTS GROUP BY EXAM_ID;

Output

+---------+------------------------+
| EXAM_ID | COUNT(DISTINCT STU_ID) |
+---------+------------------------+
|       1 |                      4 |
|       2 |                      5 |
+---------+------------------------+

Explanation

1. SELECT COUNT(DISTINCT STU_ID) FROM EXAM_RESULTS GROUP BY EXAM_ID; — It groups the EXAM_RESULTS table by EXAM_ID and uses the COUNT(DISTINCT STU_ID) function to count the number of distinct student IDs for each exam. However, the result set does not include EXAM_ID.
2. SELECT EXAM_ID, MAX(STU_ID) FROM EXAM_RESULTS GROUP BY EXAM_ID; — This query groups the results by EXAM_ID and then selects the maximum STU_ID for each exam. However, this doesn't provide the count of students who took each exam, as it gives the maximum student ID instead of counting the distinct student IDs.
3. SELECT EXAM_ID, COUNT(DISTINCT STU_ID) FROM EXAM_RESULTS GROUP BY EXAM_ID; — It groups the EXAM_RESULTS table by EXAM_ID and uses the COUNT(DISTINCT STU_ID) function to count the number of distinct student IDs for each exam. The result set includes the EXAM_ID and the count of students who took each exam.
4. SELECT EXAM_ID, MIN(STU_ID) FROM EXAM_RESULTS GROUP BY EXAM_ID; — This query groups the results by EXAM_ID and selects the minimum STU_ID for each exam. It does not provide information about the number of students who took each exam.